1. H. Huang Transparency No.7-1 The 68HC11 Microcontroller Chapter 7: Parallel I/O Ports The 68HC11 Microcontroller Han-Way Huang Minnesota State University, Mankato

2. H. Huang Transparency No.7-2 The 68HC11 Microcontroller Basic I/O Concepts Peripheral devices Pieces of equipment that exchange data with a computer. Examples include switches, light-emitting diodes, cathode-ray tube screens, printers, modems, keyboards, and disk drives. Interface (peripheral) chip -A chip whose function is to synchronize data transfer between the CPU and I/O devices. -An interface may consist of control registers, status registers, data direction latches, and control circuitry. -An interface chip has pins that are connected to the CPU and I/O port pins that are connected to the I/O devices. -Each interface chip has a chip enable signal input or inputs, when asserted, allow the interface chip to react to the data transfer request. -Data transfer between an I/O device and the CPU can be proceeded bit-by-bit or in multiple bits.

3. H. Huang Transparency No.7-3 The 68HC11 Microcontroller

4. H. Huang Transparency No.7-4 The 68HC11 Microcontroller I/O Schemes 1.Isolated I/O scheme -The microprocessor has dedicated instructions for I/O operations -The microprocessor has a separate address space for I/O devices 2.Memory-mapped I/O scheme -The microprocessor uses the same instruction set for I/O operations -The I/O devices and memory components are resident in the same memory space

5. H. Huang Transparency No.7-5 The 68HC11 Microcontroller I/O Transfer Synchronization The role of an interface chip 1.Synchronizing data transfer between CPU and interface chip. 2. Synchronizing data transfer between interface chip and I/O device.

6. H. Huang Transparency No.7-6 The 68HC11 Microcontroller Synchronizing the Microprocessor and the Interface Chip The polling method 1.for input -- the microprocessor checks a status bit of the interface chip to find out if the interface chip has received new data from the input device. 2.for output -- the microprocessor checks a status bit of the interface chip to find out if it can send new data to the interface chip. The interrupt-driven method 1.for input -- the interface chip interrupts the microprocessor whenever it has received new data from the input device. 2.for output -- the interface chip interrupts the microprocessor whenever it can accept new data from the microprocessor.

7. H. Huang Transparency No.7-7 The 68HC11 Microcontroller Synchronizing the Interface Chip and the I/O Devices Brute-force method -- useful when the data timing is unimportant 1.for input -- nothing special is done. The microprocessor reads the interface chip and the interface chip returns the voltage levels on the input port pins to the microprocessor. 2.for output -- nothing special is done. The interface chip places the data that it received from the microprocessor directly on the output port pins. The strobe method -- a strobe signal is used to indicate that data are stable on I/O port pins 1.for input -- the interface chip latches the data into its data register using the strobe signal. 2.for output -- the interface chip places the data on port pins that it received from the microprocessor and asserts the strobe signal. The output device latches the data using the strobe signal. The handshake method -- used when timing is crucial -two handshake signals are used to synchronize the data transfer. One signal, call it H1, is asserted by the interface chip. The other signal, call it H2, is asserted by the I/O device. -two handshake modes are available -- pulse mode and interlocked mode.

8. H. Huang Transparency No.7-8 The 68HC11 Microcontroller Input Handshake Protocol Step 1. The interface chip asserts (or pulses) H1 to indicate its intention to input data. Step 2. The input device puts data on the data port pins and also asserts (or pulses) the handshake signal H2. Step 3. The interface chip latches the data and de-asserts H1. After some delay, the input device also de-asserts H2.

9. H. Huang Transparency No.7-9 The 68HC11 Microcontroller Output Handshake Protocol Step 1. The interface chip places data on the port pins and asserts (or pulses) H1 to indicate that it has valid data to be output. Step 2. The output device latches the data and asserts (or pulses) H2 to acknowledge the receipt of data. Step 3. The interface chip de-asserts H1 following the assertion of H2. The output device then de-asserts H2.

10. H. Huang Transparency No.7-10 The 68HC11 Microcontroller 68HC11 Parallel I/O Overview -The 68HC11A8 has 40 I/O pins that are arranged in five I/O ports. -All I/O pins serve multiple functions. -Ports A, B, and E with the exception of port A pin 7 are fixed-direction inputs or outputs. -Ports C and D are bi-directional I/O pins under the control of their associated data direction registers. -Port C, port B, the STRA pin, and the STRB pin are used for strobed and handshake parallel I/O, as well as for general-purpose I/O. Port Registers -To input, the 68HC11 reads from the port data register -To output, the 68HC11 writes into the port data register -All except port C have one data register: PORTA (at $1000) PORTB (at $1004) PORTC (at $1003) PORTCL (at $1005) PORTD (at $1008) PORTE (at $100A)

11. H. Huang Transparency No.7-11 The 68HC11 Microcontroller Fixed Direction I/O (ports A, B, and E) To input from an input port, execute a load instruction with the port data register as the source operand. For example, the following instruction sequence reads a byte from port E: REGBASequ$1000; I/O register block base address PORTEequ$0A; offset of port E data register from REGBAS ldx#REGBAS ldaaPORTE,X To output a byte to an output port, write to the port data register directly. For example, the following instruction sequence outputs the value #$38 to port B: REGBASequ$1000; I/O register block base address PORTBequ$04; offset of port B data register from REGBAS ldx#REGBAS ldaa#$38 staaPORTB,X

12. H. Huang Transparency No.7-12 The 68HC11 Microcontroller Bi-directional I/O (Ports C and D) -Each pin of ports C and D has an associated bit in a specific data register and another in a data direction register. -The primary direction of a pin is set by its associated bit in the data direction register. -When an output pin is read, the value at the input to the pin driver is returned. -The data direction registers are cleared by reset to configure all bi-directional I/O pins for input. -Before performing I/O operation to these two ports, the software should set up the data direction registers of these two ports.

13. H. Huang Transparency No.7-13 The 68HC11 Microcontroller Example 7.1 Write an instruction sequence to output the value $CD to port D. Solution: REGBASequ$1000 PORTDequ$08 DDRDequ$09 ldx#REGBAS ldaa#$3F; set up the directions of port D pins staaDDRD,X; “ ldaa#$CD; output $CD to port D staaPORTD,X ;“ In C language, DDRD = 0x3F;/* configure port D for output */ PORTD = 0xCD; /* output data to port D */

14. H. Huang Transparency No.7-14 The 68HC11 Microcontroller Parallel I/O Control Register (PIOC) -All strobed mode I/O and handshake I/O are controlled by this register

15. H. Huang Transparency No.7-15 The 68HC11 Microcontroller Strobe Input Port C -Strobe mode I/O is selected when the bit 4 of the PIOC register is set to 0 and port C becomes a strobe input port. -The bit 1 of the PIOC register selects the active edge of the STRA pin. -The active edge of the STRA signal latches the values of the port C pins into the PORTCL register. -Reading the PORTC register returns the current values on the port C pins. -Reading the PORTCL register returns the contents of the latched PORTCL. -When enabled, the active edge of the STRA signal will generate an interrupt to the 68HC11.

16. H. Huang Transparency No.7-16 The 68HC11 Microcontroller Strobed Output Port B The strobe signal STRB is pulsed for two E clock cycles each time there is a write to port B.

17. H. Huang Transparency No.7-17 The 68HC11 Microcontroller Port C Input Handshake Protocol -STRA is a latch command asserted by an input device (active edge is rising in the figure). -STRB is a ready output driven by the 68HC11 (active high in the figure). -When ready for accepting new data, the 68HC11 asserts (or pulses) STRB pin. -The input device places data on input port pins and asserts the STRA signal. The active edge of STRA latches data into the PORTCL register, sets the STAF flag in PIOC register and de-asserts the STRB signal. The de-assertion of STRB inhibits external device from strobing new data into port C. -Not until the 68HC11 reads PORTCL, new data cannot be applied on port C pins.

18. H. Huang Transparency No.7-18 The 68HC11 Microcontroller Port C Output Handshake Protocol -STRA is an acknowledge input (driven by the external device) -STRB is a ready output (driven by the 68HC11) -In this figure, the active edge of STRA is rising and the active level of STRB is high. -The 68HC11 writes data into PORTCL and then asserts STRB to indicates there are valid data on port C pins -The external device then asserts STRA to acknowledge the receipt of data which will then cause STRB to be de-asserted and the STAF flag to be set. -After the de-assertion of STRB, STRA is also de-asserted.

19. H. Huang Transparency No.7-19 The 68HC11 Microcontroller Simple Input Devices: switches, analog-to-digital converter, keyboards, etc. Example 6.2 Connect an 8-DIP switch to port E of the 68HC11 and read a byte from it. Solution: REGBASequ $1000 PORTEequ $0A LDX #REGBAS LDAA PORTE,X. In C #include main () { char xx; … xx = PORTE; … }

20. H. Huang Transparency No.7-20 The 68HC11 Microcontroller Interfacing Parallel Ports to the Keyboard -A keyboard is arranged as an array of switches, which can be mechanical, membrane, capacitive, or Hall-effect in construction. -In mechanical switches, two metal contacts are brought together to complete a circuit. -Mechanical switches have a problem called contact bounce. A series of pulses are generated because the switch contacts do not come to rest immediately. -The response time of the switch is several orders of magnitude slower than that of a computer. -A debouncing process is needed to solve the contact bounce problem. Keyboard input procedure Step 1. Keyboard scanning to find out which key has been pressed. Step 2. Key debouncing to make sure a key was pressed. Step 3. Table lookup to find the ASCII code of the key that has been pressed.

21. H. Huang Transparency No.7-21 The 68HC11 Microcontroller Keyboard Scanning Techniques -A keyboard with more than a few keys is often arranged as a matrix of switches that uses two decoding and selecting devices to determine which key was pressed. - An example of 64-key keyboard is shown in Figure 7.13. -The MC14051 is an analog multiplexor and is used to select the row. -The 74LS138 selects the column. -PC5-PC3 select the row and PC2-PC0 select the column to be scanned. -X7-X0 are pulled up to 5 V by the pull-up resistors. -The decoder 74LS138 outputs are asserted low. -A pressed key will send a low to the X output to the port C pin 7 and hence can be detected.

22. H. Huang Transparency No.7-22 The 68HC11 Microcontroller Keyboard Scanning Algorithm - The basic algorithm is shown in Figure 7.14. - Since we use port C pin 0 to 2 to select the column and pin 3 to 5 to select the row, we can use the INC PORTC,X instruction to move to the next key. This is done in the program on next page.

23. H. Huang Transparency No.7-23 The 68HC11 Microcontroller The program to scan the keyboard in Figure 7.13 Pins PC7 should be configured for input while PC5-PC0 should be configured for output. REGBASequ$1000; base address of I/O register block DDRCequ$07; offset of port C data direction register from REGBAS KEYBDequ$03; port C is used as keyboard ldaa#$3F; set up port C pin directions staaDDRC,X;“ resetcclrKEYBD,X; start from row 0 and column 0 scanbrclrKEYBD,X $80 debnce ; detect a pressed key brsetKEYBD,X $3F resetc ; need to reset the row and column count incKEYBD,X; check the next row or column brascan end

24. H. Huang Transparency No.7-24 The 68HC11 Microcontroller Keyboard Debouncing - The signal output from the key switch falls and rises a few times within a period of 5 ms as the contact bounces. - A human being cannot press and release a key in less than 20 ms, a debouncer will recognize that the switch is closed/open after the voltage is low/high for 10 ms. - Both hardware and software debouncing techniques are available. Hardware debouncing techniques 1.Set-reset flip-flops 2.Non-inverting CMOS gates with high-input impedance 3.Integrating debouncers

25. H. Huang Transparency No.7-25 The 68HC11 Microcontroller Software Debouncing Techniques The easiest software debouncing technique is the wait-and-see technique. After detecting a key switch has been pressed, this technique simply wait for 10 ms and recheck the same key. REGBASequ$1000; base address of the I/O register block KEYBDequ$03; offset of PORTC from REGBAS TEN_MSequ2000; loop count for creating 10 ms delay debnceldy#REGBAS ldx#TEN_MS wait10msnop; wait for 10 ms nop;“ dex;“ bnewait10ms;“ ldaaKEYBD,X; recheck the pressed key bmiscan; rescan the keyboard if the key is not pressed jmpgetcode; the key switch is indeed pressed end

26. H. Huang Transparency No.7-26 The 68HC11 Microcontroller ASCII Code Table Lookup After the key has been debounced, the keyboard should look up the ASCII table and send the corresponding ASCII code to the CPU. keytabFCC“0123456789” FCC.... FCC… getcodeLDX#REGBAS LDABKEYBD,X CLRA ANDB#$3f; compute the address of the ASCII code of the pressed ADDD#keytab; key and leave it in X XGDX;“ LDAA0,X; get the ASCII code END

27. H. Huang Transparency No.7-27 The 68HC11 Microcontroller Example 7.3 Write a C routine to read a character from the keyboard. This routine will perform keyboard scanning, debouncing, and ASCII code lookup and return the ASCII code to the caller. Solution: char get_ascii (); void delay10ms (); char tab[64] = {….};/* ASCII code table */ char read_kb () { charscanned, pressed; scanned = 0; PORTC = 0; while (1) { while (!scanned) { if (PORTC & 0X80) {/* If key is not pressed */ if ((PORTC & 0x3F) == 0x3F) /* read row 7 and column 7 */ PORTC = 0x00;/* reset to row 0 column 0 */ else PORTC ++; /* scan the next key */ }

28. H. Huang Transparency No.7-28 The 68HC11 Microcontroller else scanned = 1;/* detect a pressed key */ } delay10ms ();/* wait for 10 ms to recheck the same key */ if (!(PORTC &0x80)) return (get_ascii ());/* the key is really pressed */ else { scanned = 0; } /* the following subroutine use OC2 function to create a 10 ms delay */ void delay10ms () { TFLG1 = 0x40;/* clear OC2F */ TOC2 = TCNT + 20000;/* start an OC2 operation to create 10 ms delay */ while (!(TFLG1 & 0x40));/* wait until 10 ms is over */ } char get_ascii () { char i; i = PORTC & 0x3F;/* obtain the row and column number for table lookup */ return tab[i]; }

29. H. Huang Transparency No.7-29 The 68HC11 Microcontroller Interfacing 68HC11 with a Keypad -People are using 12- to 24-key keypad for many applications. -An example of 16-key membrane keypad is shown in Figure 7.16. The row selection is shown in Table 7.4.

30. H. Huang Transparency No.7-30 The 68HC11 Microcontroller Example 7.4 Write a C program to read a character from the keypad shown in Figure 7.16. This program will perform keypad scanning, debouncing, and ASCII code lookup. Solution: void wait_10ms ( ); char get_key ( ) { DDRC = 0xF0;/* configure PC7-PC4 for output and PC3-PC0 for input */ while (1){ PORTC = 0xE0;/* prepare to scan the row controlled by PC4 */ if (!(PORTC & 0x01)) { wait_10ms ( ): if (!(PORTC & 0x01)) return 0x30;/* return ASCII code of 0 */ } if (!(PORTC & 0X02)) { wait_10ms ( ): if (!(PORTC & 0x02)) return 0x31;/* return ASCII code of 1 */ }

31. H. Huang Transparency No.7-31 The 68HC11 Microcontroller if (!(PORTC & 0X04)) { wait_10ms ( ): if (!(PORTC & 0x04)) return 0x32;/* return ASCII code of 2 */ } if (!(PORTC & 0X08)) { wait_10ms ( ): if (!(PORTC & 0x08)) return 0x33;/* return ASCII code of 3 */ } PORTC = 0xD0;/* set PC5 to low to scan second row */ if (!(PORTC & 0X01)) { wait_10ms ( ): if (!(PORTC & 0x01)) return 0x34;/* return ASCII code of 4 */ } if (!(PORTC & 0X02)) { wait_10ms ( ): if (!(PORTC & 0x02)) return 0x35;/* return ASCII code of 5 */ }

32. H. Huang Transparency No.7-32 The 68HC11 Microcontroller if (!(PORTC & 0X04)) { wait_10ms ( ): if (!(PORTC & 0x04)) return 0x36;/* return ASCII code of 6 */ } if (!(PORTC & 0X08)) { wait_10ms ( ): if (!(PORTC & 0x08)) return 0x37;/* return ASCII code of 7 */ } PORTC = 0xB0;/* set PC6 to low to scan the third row */ if (!(PORTC & 0X01)) { wait_10ms ( ): if (!(PORTC & 0x01)) return 0x38;/* return ASCII code of 8 */ } if (!(PORTC & 0X02)) { wait_10ms ( ): if (!(PORTC & 0x02)) return 0x39;/* return ASCII code of 8 */ }

33. H. Huang Transparency No.7-33 The 68HC11 Microcontroller if (!(PORTC & 0X04)) { wait_10ms ( ): if (!(PORTC & 0x04)) return 0x41;/* return ASCII code of A */ } if (!(PORTC & 0X08)) { wait_10ms ( ): if (!(PORTC & 0x08)) return 0x42;/* return ASCII code of B */ } PORTC = 0x70;/* set PC7 to low to scan the fourth row */ if (!(PORTC & 0X01)) { wait_10ms ( ): if (!(PORTC & 0x01)) return 0x43;/* return ASCII code of C */ } if (!(PORTC & 0X02)) { wait_10ms ( ): if (!(PORTC & 0x02)) return 0x44;/* return ASCII code of D */ }

34. H. Huang Transparency No.7-34 The 68HC11 Microcontroller if (!(PORTC & 0X04)) { wait_10ms ( ): if (!(PORTC & 0x04)) return 0x45;/* return ASCII code of E */ } if (!(PORTC & 0X08)) { wait_10ms ( ): if (!(PORTC & 0x08)) return 0x46;/* return ASCII code of F */ }

35. H. Huang Transparency No.7-35 The 68HC11 Microcontroller Simple Output Devices A Single Light-Emitting Diode (LED) -An LED will illuminate when it is forward biased and has enough current flowing through it. -The current required to light an LED brightly ranges from a few mA to more than ten mA. -The voltage drop across a forward-biased LED ranges from 1.7V to more than 2 V. -The voltage drop across the LED with 10 mA current flowing through it is assumed to be 1.7V in this chapter. -In Figure 7.17, the 74HC04 has an high output 4.9V and a low output 0.1V. A high applied to the input of 74HC04 will light the LED. -The 68HC11 does not have the current capability to drive the LED. A chip like the 74HC04 is needed to provide the required current capability.

36. H. Huang Transparency No.7-36 The 68HC11 Microcontroller Example 7.5 Use the 68HC11 port B pins PB3, PB2, PB1, and PB0 to drive blue, green, red, and yellow LEDs. Light the blue LED for 2 s, then the green LED for 4 s, then the red LED for 8 s, and finally the yellow LED for 16 seconds. Repeat this operation forever. Solution: The circuit is shown in Figure 7.18. -To light the blue LED, output $08 to port B. -To light the green LED, output $04 to port B. -To light the red LED, output $02 to port B. -To light the yellow LED, output $01 to port B. -The required time can be created by repeating the following delay loop for 20, 40, 80, and 160 times: ldx #20000 tenth_snop nop dex bne tenth_s

37. H. Huang Transparency No.7-37 The 68HC11 Microcontroller regbasequ $1000 portbequ $04 org $00 lt_tabfcb 20,$08,40,$04,80,$02,160,$01 org $C000 loopldy #lt_tab nextldab 0,Y ; get the repetition count ldaa 1,Y ; get the light pattern iny ldx #regbas staa portb,X pt_lpldx #20000 tenth_snop nop dex bne tenth_s decb bne pt_lp cpy #lt_tab+8 ; reach the table end? bne next bra loop end The Program:

38. H. Huang Transparency No.7-38 The 68HC11 Microcontroller The Seven-Segment Display -A seven-segment display consists of seven LED segments (a, b, c, d, e, f, and g). -A seven-segment display can be found in common-cathode or common-anode type.

39. H. Huang Transparency No.7-39 The 68HC11 Microcontroller Driving the seven-segment displays with the 68HC11 parallel ports -A segment requires 10 mA to be lighted brightly. -A buffer chip like 74ALS244 can be used to boost the 68HC11’s current capability. -The 74ALS244 has a 3V output when it is high and a 0.2V output when it is low. -For the circuit shown in Figure 7.20, a segment will have a current of 13 mA when it is lighted. -To display a BCD digit, an appropriate value must be written to the port register. The value is listed in Table 7.6. -When multiple digits are to be displayed, the multiplexing technique is often used to reduce the number of port pins required.

40. H. Huang Transparency No.7-40 The 68HC11 Microcontroller Using Multiplexing Method to Display Multiple BCD Digits -The 2N2222 can sink 100-300 mA of current and can handle the maximum current (91 mA) flowing into the collector from the common cathode. -To light seven-segment display #5, send out the segment pattern to port B and output the value $20 to port D. -To light display #4, send out the segment pattern to port B and output the value $10 to port D. -etc.

41. H. Huang Transparency No.7-41 The 68HC11 Microcontroller How the Multiplexing Method Works -To light the display #5,…,#0, the corresponding value to be written into port D are $20, $10, $08, $04, $02, and $01 respectively. For example, the following instruction sequence will display the digit 6 on the display #3: REGBASequ$1000; base address of I/O register block PORTBequ$04; offset of PORTB from REGBAS PORTDequ$08; offset of PORTD from REGBAS DDRDequ$09; offset of DDRD from REGBAS sixequ$7D; segment pattern of 6 thirdequ$08; value to allow display #3 to light outputequ$3F org$C000 ldx#REGBAS ldaa#output; configure port D for output staaddrd,X;“ ldaa#six; send the segment pattern of 6 to port B staaPORTB,X;“ ldaa#third; select display #3 to be lighted staaPORTD,X;“ end

42. H. Huang Transparency No.7-42 The 68HC11 Microcontroller In C language, DDRD = 0x3F; PORTB = 0x5F; PORTD = 0x08; Principle of Multiplexing multiple displays: Persistence of vision. As long as one and only one display is lighted and then turned off for a short period of time within one second all digits will appear to be lighted simultaneously.

43. H. Huang Transparency No.7-43 The 68HC11 Microcontroller Example 7.6 Display 123456 on the six seven-segment displays shown in Figure 7.21. Solution: The first step is to build a table of segment patterns (to port B) and display selection values (to port D). This Table can be set up by the following assembler directives: org $00 displayFCB$06,$20 FCB$5B,$10 FCB$4F,$08 FCB$66,$04 FCB$6D,$02 FCB$7D,$01

44. H. Huang Transparency No.7-44 The 68HC11 Microcontroller Algorithm for Displaying Multiple Digits Using Time Multiplexing Technique

45. H. Huang Transparency No.7-45 The 68HC11 Microcontroller regbasequ $1000 PORTBequ $04 PORTDequ $08 DDRD equ $09 outputequ $3F org $00 displayfcb $06,$20 fcb $5B,$10 fcb $4F,$08 fcb $66,$04 fcb $6D,$02 fcb $7D,$01 org $C000 ldx #regbas ldaa #output staa ddrd,X foreverldy #display nextldaa 0,Y ldx #regbas staa PORTB,X ldaa 1,Y staa PORTD,X iny ldx #200 ; loop to delay for 1 ms againnop;“ nop;“ dex;“ bne again;“ cpy #display+12 ; end of table? beq forever bra next; light the next display end

46. H. Huang Transparency No.7-46 The 68HC11 Microcontroller C language version #include char display [6][2] ={{0x30, 0x20}, {0x6D, 0x10}, {0x79, 0x08}, {0x33, 0x04}, {0x5B, 0x02}, {0x5F, 0x01}}; void delay_1ms ( ); main ( ) { inti; while (1) { for (i = 0; i < 6; i++) { PORTB = display[i][0]; PORTD = display[i][1]; delay_1ms ( ); } void delay_1ms ( ) { TFLG1 = 0x40;/* clear OC2F flag */ TOC2 = TCNT + 2000; while (!(TFLG1 & 0x40)); }

47. H. Huang Transparency No.7-47 The 68HC11 Microcontroller Liquid Crystal Displays (LCD) -An LCD must be activated in order to be lighted. -The LCD type of display that is most common today allows light to pass through it when it is activated. -The LCD displays are organized as segments for displaying digits or characters. -Activation of a segment requires a low-frequency bipolar excitation voltage of 30-1000 Hz. -When a voltage is placed across the segment, an electric field is set up which aligns the crystals in the liquid. This alignment allows the light to pass through. -A segment which is not aligned will reflect the light. -The LCD has very high contrast and can be seen extremely well in very bright light. -The main problem of LCD is that it requires light source in dim or dark area because it produces no light of its own.

48. H. Huang Transparency No.7-48 The 68HC11 Microcontroller Optrex DMC-20434 LCD Kit -4  20 LCD kit that uses Hitachi HD44780 as its display controller. -Can be used with all demo boards manufactured by Axiom Manufacturing. -DB7-DB0 are used to exchange data with the microcontroller. -E pin is the enable signal to the LCD. -RS selects the signal to be accessed. -In CMD-11A8, the address $B5F0 is assigned to the control register and the address $B5F1 is assigned to data register.

49. H. Huang Transparency No.7-49 The 68HC11 Microcontroller The Setup of the DMC-20434 LCD kit -All LCD kits need to be set up before they can be used. -To set up the LCD kit, we need to write appropriate commands into the command register. -Commands for the LCD kit are listed in table 7.8.

50. H. Huang Transparency No.7-50 The 68HC11 Microcontroller Program to initialize the DMC-20434 LCD kit lcd_cmd EQU$B5F0 lcd_initPSHX LDX#lcd_cmd BRSET0,X $80 * LDAA#$3C STAA0,X; set 4  20 display BRSET0,X $80 *; wait until LCD is ready LDAA#$01 STAA0,X; clear display and move cursor to home BRSET0,X $80 * LDAA#$0F STAA0,X; turn on display BRSET0,X $80 * LDAA#$06 STAA0,X; set cursor increment, shift off BRSET0,X $80 * LDAA#$14 STAA0,X; set cursor shift right BRSET0,X $80 *

51. H. Huang Transparency No.7-51 The 68HC11 Microcontroller LDAA#$02 STAA0,X BRSET0,X $80 * PULX RTS In C language, we need to add the following two lines to the hc11.h file in the ImageCraft C compiler so that we can use LCD_CMD and LCD_DAT to access the registers of the LCD kit: #defineLCD_CMD *(unsigned char volatile *)(0xB5F0) #defineLCD_DAT *(unsigned char volatile *)(0xB5F1)

52. H. Huang Transparency No.7-52 The 68HC11 Microcontroller The C language version of the LCD kit initialization function: void lcd_init ( ) { while (LCD_CMD & 0x80);/* wait while LCD is busy */ LCD_CMD = 0x3C;/* set 4  20 display */ while (LCD_CMD & 0x80); LCD_CMD = 0x01;/* clear display and set cursor to home */ while (LCD_CMD & 0x80); LCD_CMD = 0x0F;/* display cursor, and cursor blink on */ while (LCD_CMD & 0x80); LCD_CMD = 0x06;/* set cursor increment, shift off */ while (LCD_CMD & 0x80); LCD_CMD = 0x14;/* set cursor shift right */ while (LCD_CMD & 0x80); LCD_CMD = 0x02;/* move cursor to home */ while (LCD_CMD & 0x80); }

53. H. Huang Transparency No.7-53 The 68HC11 Microcontroller Output Data on the DMC-20434 LCD Kit -The DMC-20434 does not display alphanumeric data in sequential order due to its internal line wrapping. -Without line adjustment, the LCD kit will display the first 20 characters in the first line, the second 20 characters in the third line, the third 20 characters in the second line, and the fourth 20 characters in the fourth line. -The following subroutine outputs one character to the LCD kit and performs line adjustment: LCD_CMDEQU$B5F0; LCD command register address LCD_DATEQU$B5F1; LCD data register address lcdputch2lcdSTAALCD_DAT; output 1 character to the LCD kit lcdlpLDAALCD_CMD; read next character position BMIlcdlp; test if busy and wait if true CMPA#$13; test for line 1 wrap BEQlcd1; if match, correct line wrap CMPA#$53; test for line 2 wrap BEQlcd2; if match, correct line wrap CMPA#$27; test for line 3 wrap BEQlcd3; if match, correct line wrap RTS

54. H. Huang Transparency No.7-54 The 68HC11 Microcontroller * correct line 1 wrap from line 3 to line 2 lcd1LDAA#$40; load line 2 start position ORAA#$80; set command bit STAALCD_CMD; write to display RTS * correct line 2 wrap from line 4 to line 3 lcd2LDAA#$14; load line 3 start position ORAA#$80; set command bit STAALCD_CMD; write to display RTS * correct line 3 wrap from line 2 to line 4 lcd3LDAA#$54; load line 4 start position ORAA#$80; set command bit STAALCD_CMD; write to display RTS * this is the program to output a string pointed by Y and terminated by a NULL character putstr2lcdLDAA0,Y BEQdone JSRputch2lcd INY BRAputstr2lcd doneRTS

55. H. Huang Transparency No.7-55 The 68HC11 Microcontroller C Language Version of LCD Output Functions void putch2lcd (char ch) { LCD_DAT = ch; while (LCD_CMD & 0x80); if (LCD_CMD == 0x13) { LCD_CMD = 0x40 || 0x80;/* correct line 1 wrap from line 3 to line 2 */ while (LCD_CMD & 0x80); } if (LCD_CMD == 0x53) {/* correct line 2 wrap from line 4 to line 3 */ LCD_CMD = 0x14 || 0x80; while (LCD_CMD & 0x80); } if (LCD_CMD == 0x27) {/* correct line 3 wrap from line 2 to line 4 */ LCD_CMD = 0x54 || 0x80; while (LCD_CMD & 0x80); }

56. H. Huang Transparency No.7-56 The 68HC11 Microcontroller void putstr2lcd (char *ptr) { while (*ptr) { putch2lcd (*ptr); ptr++; }

57. H. Huang Transparency No.7-57 The 68HC11 Microcontroller Digital to Analog Converter -D/A conversion is required when a digital code must be converted to an analog signal. -A general D/A converter consists of a network of precision resistors, input switches, and level shifters that activate the switches that convert a digital code to an analog voltage or current. -D/A converters have a fixed or variable reference voltage, which can be generated either internally or externally. -The reference voltage determines the switching threshold of the precision switches that form the impedance network that controls the value of the output signal. -Fixed reference D/A converts have current or voltage output values that are proportionally to the digital input. -Multiplying D/A converters produce an output signal that is proportional to the product of a varying reference level and a digital code.

58. H. Huang Transparency No.7-58 The 68HC11 Microcontroller Interfacing to the D/A Converter Using the 68HC11 Output Ports -The AD557 is an 8-bit D/A converter that produces an output voltage proportional to the digital input code. -The AD557 can operate with a +5V supply. -Output range is 0V to +2.55V when operated as shown in Figure 6.23. -Vout = (decimal equivalent of input code) × 0.01 V

59. H. Huang Transparency No.7-59 The 68HC11 Microcontroller AD557 Input latch operation -Data input can be latched or transparent without being latched. -The CS and CE signals together control the latching of input data. The AD557 can be used to generate analog waveforms as illustrated in the next example. It takes 1  s to complete the conversion of one sample.

60. H. Huang Transparency No.7-60 The 68HC11 Microcontroller Example 7.8 Use the 68HC11 port B and an AD557 to generate a sawtooth waveform. Solution: The circuit connection is shown in Figure 7.28. The program is in the following: regbasequ $1000 PORTBequ $04 org $C000 ldx #regbas clr PORTB,X againinc PORTB,X bra again end In C language, #include main ( ) { PORTB = 0; while (1) { POTB ++; }

61. H. Huang Transparency No.7-61 The 68HC11 Microcontroller Example 7.9 Using the circuit in Figure 7.28 to generate the waveform shown in Figure 7.29. Solution: REGBASEQU$1000 PORTBEQU$04 ORG$C000 LDY#REGBAS startCLRPORTB,Y; output 0V JSRdelay_1ms; wait for 1 ms LDAA#100; output 1 V JSRdelay_1ms LDAA#200; output 2 V JSRdelay_1ms BRAstart delay_1msLDX#200 againNOP NOP DEX BNEagain RTS

62. H. Huang Transparency No.7-62 The 68HC11 Microcontroller The C Program to Generate the waveform shown in Figure 7.29. #include void delay_1ms ( ); main ( ) { while (1) { PORTB = 0;/* output 0 V */ delay_1ms ( );/* wait for 1 ms */ PORTB = 100;/* output 1 V */ delay_1ms ( ); PORTB = 200;/* output 2 V */ delay_1ms ( ); } return 0; } void delay_1ms ( ) { TFLG1 = 0x40;/* clear OC2F flag */ TOC2 = TCNT + 2000; /* start an OC2 operation with 1 ms delay */ While (!(TFLG1 & 0x40)); /* wait for 1 ms */ }

63. H. Huang Transparency No.7-63 The 68HC11 Microcontroller Centronics Printer Interface Signals: D7-D1: data pins. BUSY: printer busy signal (output from printer) PE: printer error (asserted high). SLCT: printer on-line (output from printer) DATA STROBE: An input to the printer. Data is latched into the printer by this signal. ACKNLG: Printer acknowledges the receipt of data using this signal. Centronics printer timing requirements

64. H. Huang Transparency No.7-64 The 68HC11 Microcontroller Interface a Centronics printer to the 68HC11 port C Configure port C as follows: 1.Set port C for output, i.e., write the value $FF into DDRC. 2.Program PIOC to set the following parameters: pulse mode handshake output no STRA interrupt falling edge of STRA as the active edge STRB is active low normal port C pins Write the value $1C into PIOC. Data setup time is period of E ÷ 2 - t PWD + t DEB = 325 ns > 50 ns (required) Data hold time (with respect to DATA STROBE) is at least 2 E clock cycles (= 1  s at 2 MHz). This is greater than the 100 ns requirement. The timing requirements are satisfied :

65. H. Huang Transparency No.7-65 The 68HC11 Microcontroller For the following subroutines, use these constant declarations: regbasequ $1000 ; base address of I/O register block DDRCequ $07 ; offset of DDRC from regbas PIOCequ $02 ; offset of PIOC from regbas PORTCLequ $05 ; offset of PORTCL from regbas PORTEequ $0A ; offset of PORTE from regbas outputequ $FF ; value to set port C as an output port Write a routine to initialize the Centronics printer in Figure 7.32. prt_initpsha pshx ldx #regbas brset PORTE,X $40 * ; don’t go if printer error brclr PORTE,X $80 * ; don’t go if printer not on-line ldaa #output ; configure port C for output staa DDRC,X ;“ ldaa #$1C ; initialize PIOC staa PIOC,X ;“ pulx pula rts

66. H. Huang Transparency No.7-66 The 68HC11 Microcontroller Write subroutines to print a character and a string using polling method The subroutine prt_char outputs the character in A. prt_charBRCLR PIOC,X $80 * ; wait until the STAF bit is set to 1 STAA PORTCL,X; print the character in A RTS The subroutine prt_str outputs the string pointed to by index register Y. The index register X contains the base address of the I/O register block. The string is terminated by a NULL character. prt_strPSHA nextLDAA 0,Y; get the next character BEQ quit; is this the end of the string? JSR prt_char; print the current character INY; move the string pointer BRA next quitPULA RTS

67. H. Huang Transparency No.7-67 The 68HC11 Microcontroller Write subroutines to print a character and a string using interrupt-driven method prt_str1: enable the interrupt and then wait for the printer interrupt until the whole string is printed. prt_char1: print the character in A and also move the string pointer Y. Set up the interrupt vector table: ORG $FFF2 FDB prt_char1 prt_str1BSET PIOC,X $40; enable STRA interrupt CLI;“ againLDAA 0,Y; wait for printer interrupt BNE again; is this end of the string BCLR PIOC,X $40; disable STRA interrupt SEI; disable all interrupt RTS prt_char1STAA PORTCL,X; print the character INY; move the string pointer TSX STY 5,X; also update the saved version of Y RTI

68. H. Huang Transparency No.7-68 The 68HC11 Microcontroller C Language Version of the Printer Routines void prt_init ( ) { while ((PORTE & 0x40) || (!(PORTE & 0x80))); DDRC = 0xFF; PIOC = 0x1C; } /* polling method version */ void prt_char (char ch) { while (!(PIOC & 0x80))); PORTCL = ch; } /* polling method version */ void prt_str (char *ptr) { while(*ptr) { prt_char (*ptr); ptr++; }

69. H. Huang Transparency No.7-69 The 68HC11 Microcontroller Interrupt-Driven Method Printer Routines - The subroutine prti_str enable printer interrupt and then stay in a wait loop to wait for printer interrupt. -The printer interrupt service routine (prti_char) outputs the character pointed by Y. -The base address of I/O register block is passed in X. -Interrupt vector table entry for STRA interrupt must be set up properly. prti_strBSETPIOC,X $40; enable STRA interrupt CLI againLDAA0,Y; wait for interrupt BNEagain; reach the end of the string? BCLRPIOC,X $40; disable STRA interrupt SEI RTS prti_charSTAAPORTCL,X INY TSX STY5,X; update the Y value in the stack RTI

70. H. Huang Transparency No.7-70 The 68HC11 Microcontroller C Language Version of the Interrupt-Driven Printer Functions -The pointer to the string to be output is defined as a global variable char *ptr; void prti_str ( ) { PIOC |= 0x40; /* enable STRA interrupt */ INTR_ON ( ); while (*ptr);/* wait for interrupt */ PIOC &= 0xBF;/* disable STRA interrupt */ INTR_OFF ( ); } /* STRA interrupt service routine */ #pragma interrupt_handler prti_char ( ) void prti_char () { PORTCL = *ptr++; }

71. H. Huang Transparency No.7-71 The 68HC11 Microcontroller The i8255 Programmable Peripheral Interface (PPI) -In expanded mode, both port B and port C are not available for I/O functions. -A possible solution to this problem is to add an parallel interface chip such as i8255 to the 68HC11. -The Intel i8255 has three 8-bit ports: port A, B, and C. -Signals A1-A0 select the registers within the PPI as follows:

72. H. Huang Transparency No.7-72 The 68HC11 Microcontroller Operation of the i8255 -When the msb is 1, the control register defines the operation mode. Otherwise it sets or clears a selected bit. -i8255 has three modes: mode 0, mode 1, and mode 2.

73. H. Huang Transparency No.7-73 The 68HC11 Microcontroller Mode 0 (basic input and output) -There are two 8-bit ports and two 4-bit ports. -Any port can be input or output. -Outputs are latched. -Inputs are not latched. -16 different input/output configurations are possible in this mode. -No handshake is required. -Data are simply written into or read from a specified port.

74. H. Huang Transparency No.7-74 The 68HC11 Microcontroller Mode 1 (Strobed Input/Output) -Port A and B use the lines of port C to generate or accept “handshake” signals required in this mode. -Port A, B, and C are divided into two groups. Each group consists of one 8-bit port and one 4-bit control/data port. The 8-bit data port can be input or output. The 4-bit port is used for control and status of the 8-bit data port. -Port C pin functions are shown in Table 7.10

75. H. Huang Transparency No.7-75 The 68HC11 Microcontroller Mode 1 Input Timing -When the input buffer is not full, the input device places data on input port pins and pulses the STB signal. -The falling edge of STB latches data into the input port data register and sets the input buffer full flip-flop. -The PPI asserts the interrupt request signal INTR and the CPU reads the data in the interrupt service routine. After the data is read, the input buffer full flag is cleared.

76. H. Huang Transparency No.7-76 The 68HC11 Microcontroller Mode 1 Output Timing -When the output buffer is not full and the CPU is interrupted, the CPU writes data to the i8255. For a delay of t WB after the rising edge of the WR signal, data appears on i8255 port pins. -The OBF signal is asserted by the write operation. The falling edge of the OBF latches data into the output device and the output device asserts the ACK signal to acknowledge the receipt of data.

77. H. Huang Transparency No.7-77 The 68HC11 Microcontroller Mode 2 (Strobed bi-directional bus I/O) -This mode provides a means for communication with peripheral device or structure on a single 8-bit bus for both transmitting and receiving data. -Only port A is used. Port A becomes an 8-bit bi-directional bus port whereas 5 bits (PC3-PC7) of port C are used as control port. -Functions of port C pins are shown in Table 7.11.

78. H. Huang Transparency No.7-78 The 68HC11 Microcontroller Mode 2 Signal Transactions

79. H. Huang Transparency No.7-79 The 68HC11 Microcontroller Mode 2 Data Output Polling approach -The software tests the OBF signal to determine whether the output buffer is empty. If it is, the data is written out. -The external circuitry also monitors OBF signal to decide if the microprocessor has sent new data to the i8255. As soon as OBF is detected to be low, the output device sends back the ACK signal to remove data from the output buffer. -The low level of the ACK signal causes the OBF signal to go high and enables the three- state output buffer so that data can be read. Interrupt-driven approach -The software first enables the i8255 interrupt. When the output buffer is empty, it generates an interrupt to the CPU. The CPU outputs a byte to the i8255 in the interrupt service routine. -The byte written to the i8255 causes the OBF signal to go low, which informs the output device to latch data. -The output device asserts the ACK signal to acknowledge the receipt of data, which causes the OBF signal to become inactive.

80. H. Huang Transparency No.7-80 The 68HC11 Microcontroller Mode 2 Data Input Polling approach -The software tests the IBF signal to determine if data have been strobed into the buffer. -If IBF is low, the input device places data on port A pins and asserts the STB signal to strobe data into the input buffer. After this, the IBF signal goes high. -When the user program detects that the IBF signal is high, it reads the data from the input buffer. The IBF signal goes low after the data is read. Interrupt-driven approach -The software first enables the i8255 to interrupt the CPU. -When the IBF is low, the input device places data on the port pins and asserts the STB signal to strobe data into the input buffer. -After data are strobed into the input buffer, the IBF signal is asserted and an interrupt is generated. -The CPU reads the data from the input buffer when executing the interrupt service routine. -Reading data brings the IBF signal to low, which further causes the STB signal to go high.

81. H. Huang Transparency No.7-81 The 68HC11 Microcontroller The i8255 on the CMD-11A8 Demo board -Four bytes are assigned to the i8255 on the CMD-11A8 demo board: 1.$B5F4: port A register 2.$B5F5: port B register 3.$B5F6: port C register 4.$B5F7: control register Example 7.12 Configure the i8255 on the CMD-11A8 to operate in mode 0: Port A for input Port B for output Upper port C for input Lower port C for output Solution: Bit 7: set to 1 to choose mode selectLDX $B5F4 Bit 6 & 5: set to 0 to configure port A to mode 0LDAA #$98 Bit 4: set to 1 to configure port A for inputSTAA 3,X Bit 3: set to 1 to configure upper port C for input Bit 2: set to 0 to configure port B to mode 0 Bit 1: set to 0 to configure port B for output Bit 0: set to 0 to configure lower port C for output

82. H. Huang Transparency No.7-82 The 68HC11 Microcontroller Example 7.14 Use the auxiliary port of the CMD-11A8 demo board to drive 4 seven-segment displays. Use port A of the i8255 to drive the segment pattern and use the upper four bits of port B of the i8255 to drive the display select signals. Write a program to display 1999. Solution: -The circuit is shown in Figure7.39. -Configure i8255 to mode 0. -Configure port A and B for output. -Write the value $80 into the register.

83. H. Huang Transparency No.7-83 The 68HC11 Microcontroller PPI_BASEQU$B5F4; i8255 port A data register address INIT_VALEQU$80; value to initialize i8255 PAEQU0; offset of port A from PPI_BAS PBEQU1; offset of port B from PPI_BAS ORG$2000 LDAA#INIT_VAL foreverLDY#distab nextLDX#PPI_BAS LDAA0,Y STAAPA,X; send out the digit pattern LDAB1,Y STAAPB,X; send out the select value INY LDX#200; 1 ms delay againNOP; “ NOP; “ DEX; “ BNEagain; “ CPY #distab+8 BEQforever BRAnext

84. H. Huang Transparency No.7-84 The 68HC11 Microcontroller distabFCB$30,$08 FCB$7B,$04 FCB$7B,$02 FCB$7B,$01 In C language, we need to add the following statements to the hc11.h file so that we can use labels to reference i8255 registers: #define PPI_PA *(unsigned char volatile *)(0xB5F4) #define PPI_PB*(unsigned char volatile *)(0xB5F5) #define PPI_PC*(unsigned char volatile *)(0xB5F6) #define PPI_CMD*(unsigned char volatile *)(0xB5F7)

85. H. Huang Transparency No.7-85 The 68HC11 Microcontroller #include char distab [4][2] = {{0x30, 0x08}, {0x7B, 0x04}, {ox7B, 0x02}, {0x7B, 0x01}}; void wait_1ms ( ); main ( ) { PPI_CMD = 0x80;/* initialize the i8255 control register */ while (1) { for (i = 0; i < 4; i++) { PPI_PA = distab[i][0];/* output segment pattern */ PPI_PB = distab[i][1];/* send out digit select */ wait_1ms ( ); } return 0; } /* create 1 ms delay */ void wait_1ms ( ) { TFLG1 = 0x40;/* clear OC2F flag */ TOC2 = TCNT + 2000; while (!(TFLG1 & 0x40)); }

86. H. Huang Transparency No.7-86 The 68HC11 Microcontroller The 68HC24 Port Replacement Unit -In the early years of the 68HC11, the amount of on-chip EPROM or EEPROM that can be implemented onto the microcontroller chip is very limited. -The software of the target embedded product was to be placed in the on-chip ROM. -During the product development stage, software need to be modified many times. The expanded mode must be chosen and external EPROM must be used so that software can be modified and tested. -Ports B and C, which were needed in the final product, were lost in the expanded mode during the product development phase. -The port replacement unit 68HC24 was designed to regain ports B and C so that the products can be evaluated and tested. -After the design had been tested and evaluated to be satisfactory, the software in the external EPROM could be moved into the internal ROM without modification as long as the external EPROM and internal ROM occupied the same memory space. -The signals and an example of the 68HC24 application is shown in Figure 7.38.

87. H. Huang Transparency No.7-87 The 68HC11 Microcontroller 68HC11 68HC24 from reset circuit PB0-PB7 STRA STRB PC0-PC7 V DD IRQ AS AD0-AD7 CS A12-A15 E R/W RESET R/W E PB4-PB7 PB3 PC0-PC7 AS IRQ Figure 7.38 Circuit connecting the 68HC11 and the 68HC24