1. Chapter 10 HCS12 Serial Peripheral Interface

2. What is Serial Peripheral Interface (SPI)? SPI is a synchronous serial protocol proposed by Motorola to be used as standard for interfacing peripheral chips to a microcontroller. Devices are classified into the master or slaves. The SPI protocol uses four wires to carry out the task of data communication: –MOSI: master out slave in –MISO: master in slave out –SCK: serial clock –SS: slave select An SPI data transfer is initiated by the master device. A master is responsible for generating the SCK signal to synchronize the data transfer. The SPI protocol is mainly used to interface with shift registers, LED/LCD drivers, phase locked loop chips, memory components with SPI interface, or A/D or D/A converter chips.

3. The HCS12 SPI Modules An HCS12 device may have from one to three SPI modules. The MC9S12DP256 has three SPI modules: SPI0, SPI1, and SPI2. By default, the SPI0 share the use of the upper 4 Port S pins: –PS7  SS0(can be rerouted to PM3) –PS6  SCK0(can be rerouted to PM5) –PS5  MOSI0(can be rerouted to PM4) –PS4  MISO0(can be rerouted to PM2) By default, the SPI1 shares the use of the lower 4 Port P pins: –PP3  SS1 (can be rerouted to PH3) –PP2  SCK1 (can be rerouted to PH2) –PP1  MOSI1 (can be rerouted to PH1) –PP0  MISO1 (can be rerouted to PH0) By default, the SPI2 shares the use of the upper 4 Port P pins: –PP6  SS2(can be rerouted to PH7) –PP7  SCK2(can be rerouted to PH6) –PP5  MOSI2(can be rerouted to PH5) –PP4  MISO2(can be rerouted to PH4) It is important to make sure that there is no conflict in the use of signal pins when making rerouting decision.

4. SPI Related Registers (1 of 6) The operating parameters of each SPI module are controlled via two control registers: –SPIxCR1: (x = 0, 1, or 2) –SPIxCR2 The baud rate of SPI transfer is controlled by the SPIxBR register. The operation status of the SPI operation is recorded in the SPIxSR register. The contents of the SPIxCR1, SPIxCR2, SPIxBR, and SPIxSR registers are illustrated in Figure 10.1 to 10.4, respectively. The SS pin may be disconnected from SPI by clearing the SSOE bit in the SPIxCR1 register. After that, it can be used as a general I/O pin. If the SSOE bit in the SPIxCR1 register is set to 1, then the SS signal will be asserted to enable the slave device whenever a new SPI transfer is started. The equation for setting the SPI baud rate is given in Figure 10.3.

5. SPI Related Registers (2 of 6)

6. SPI Related Registers (3 of 6)

7. SPI Related Registers (4 of 6)

8. SPI Related Registers (5 of 6)

9. SPI Related Registers (6 of 6) Example 10.1 Give a value to be loaded to the SPIxBR register to set the baud rate to 2 MHz for a 24 MHz bus clock. Solution: 24 MHz  2 MHz = 12. One possibility is to set SPPR2-SPPR0 and SPR2-SPR0 to 010 and 001, respectively. The value to be loaded into the SPIxBR register is $21. Example 10.2 What is the highest possible baud rate for the SPI with 24 MHz bus clock? Solution: The highest SPI baud rate occurs when both the SPPR2-SPPR0 and SPR2-SPR0 are 000. In this case the baud rate is 24 MH  2 = 12 MHz.

10. SPI Transmission Format (1 of 3) The data bits can be shifted on the rising or the falling edge of the SCK clock. Since the SCK can be idle high or idle low, there are four possible combinations as shown in Figure 10.5 and 10.6. To shift data bits on the rising edge, set CPOL-CPHA to 00 or 11. To shift data bits on the falling edge, set CPOL-CPHA to 01 or 10. Data byte can be shifted in and out most significant bit first or least significant bit first.

11. SPI Transmission Format (2 of 3)

12. SPI Transmission Format (3 of 3)

13. Bidirectional Mode (MOMI or SISO) A mode that uses only one data pin to shift data in and out. This mode is provided to deal with peripheral devices with only one data pin. Either the MOSI pin or the MISO pin can be used as the bidirectional pin. When the SPI is configured to the master mode (MSTR bit = 1), the MOSI pin is used in data transmission and becomes the MOMI pin. When the SPI is configured to the slave mode (MSTR bit = 0), the MISO pin is used in data transmission and becomes the SISO pin. The direction of each serial pin depends on the BIDIROE bit of the SPIxCR2 register. The pin configuration for MOSI and MISO are illustrated in Figure 10.7. If one wants to read data from the peripheral device, clear the BIDIROE bit to 0. If one wants to output data to the peripheral device, set the BIDIROE bit to 1. The use of the this mode is illustrated in exercise problem 10.8.

15. Mode Fault Error If the SSx signal goes low while the SPIx is configured as a master, it indicates a system error where more than one master may be trying to drive the MOSIx and SCKx pins simultaneously. The MODF bit in the SPIxSR register will be set to 1 when mode fault condition occurs. When mode fault occurs, the MSTR bit will be cleared to 0 and the output enable for the MOSIx and SCKx pins will be deasserted.

16. SPI Circuit Connection In an SPI system, one device is configured as a master. Other devices are configured as slaves. The circuit connection for a single-slave system is shown in Figure 10.8. A multi-slave system may have two different connection methods as illustrated in Figure 10.9 and 10.10. In Figure 10.9, the master can exchange data with each individual slave without affecting other slaves. In Figure 10.10, all the slaves are configured into a larger ring. A data transmission with certain slaves will go through other slaves.

18. Example 10.3 Configure the SPI0 to operate with the following setting assuming that E clock is 24 MHz: –6 MHz baud rate –Enable SPI0 to master mode –SCK0 pin idle low with data shifted on the rising edge of SCK –Transfer data most significant bit first and disable interrupt –Disable SS0 function –Stop SPI in Wait mode –Normal SPI operation (not bidirectional mode)

19. movb#$10,SPI0BR; set baud rate to 6 MHz movb#$50,SPI0CR1; disable interrupt, enable SPI, SCK idle low, data ; latched on rising edge, data transferred msb first movb#$02,SPI0CR2; disable bidirectional mode, stop SPI in wait mode movb#0,WOMS; enable Port S pull-up Solution: f E / baud rate = 24 MHz/6 MHz = 4. We need to set SPPR2-SPPR0 and SPR2-SPR0 to 001 and 000, respectively. Write the value $10 into the SPI0BR register. –The following instruction sequence will configure the SPI0 as desired:

20. SPI Utility Functions The following operations are common in many applications and should be made into library functions to be called by many SPI applications: –Send a character to SPI  putcspix (x = 0, 1, or 2) –Send a string to SPI  putsspix (x = 0, 1, or 2) –Read a character from SPI  getcspix (x = 0, 1, or 2) –Read a string from SPI  getsspix (x = 0, 1, or 2)

21. putcspi0brclrSPI0SR,SPTEF,*; wait until write operation is permissible staaSPI0DR; output the character to SPI0 brclrSPI0SR,SPIF,*; wait until the byte is shifted out ldaaSPI0DR; clear the SPIF flag rts void putcspi0 (char cx) { char temp; while(!(SPI0SR & SPTEF)); /* wait until write is permissible */ SPI0DR = cx; /* output the byte to the SPI */ while(!(SPI0SR & SPIF)); /* wait until write operation is complete */ temp = SPI0DR;/* clear the SPIF flag */ } Function putcSPI0

22. ; the string to be output is pointed to by X putsspi0ldaa1,x+; get one byte to be output to SPI port beqdoneps0; reach the end of the string? jsrputcspi0; call subroutine to output the byte braputsspi0; continue to output doneps0rts void putsspi0(char *ptr) { while(*ptr) { /* continue until all characters have been output */ putcspi0(*ptr); ptr++; } Function putsSPI0

23. ; This function reads a character from SPI0 and returns it in accumulator A getcspi0brclrSPI0SR,SPTEF,*; wait until write operation is permissible staaSPI0DR; trigger eight clock pulses for SPI transfer brclrSPI0SR,SPIF,*; wait until a byte has been shifted in ldaaSPI0DR; return the byte in A and clear the SPIF flag rts char getcspi0(void) { while(!(SPI0SR & SPTEF)); /* wait until write is permissible */ SPI0DR = 0x00; /* trigger 8 SCK pulses to shift in data */ while(!(SPI0SR & SPIF)); /* wait until a byte has been shifted in */ return SPI0DR; /* return the character */ } Function getcSPI0

24. ; This function reads a string from the SPI and store it in a buffer pointed to by X ; The number of bytes to be read in passed in accumulator B getsspi0tstb; check the byte count beqdonegs0; return when byte count is zero jsrgetcspi0; call subroutine to read a byte staa1,x+; save the returned byte in the buffer decb; decrement the byte count bragetsspi0 donegs0clr0,x; terminate the string with a NULL character rts void getsspi0(char *ptr, char count) { while(count) { /* continue while byte count is nonzero */ *ptr++ = getcspi0(); /* get a byte and save it in buffer */ count--; } *ptr = 0; /* terminate the string with a NULL */ } Function getsSPI0

25. The HC595 Shift Register The HC595 consists of an 8-bit shift register and a D-type latch with three-state parallel output. The shift register provides parallel data to the latch. The maximum data shift rate is 100 MHz (Philips part).

26. Signal Pins of the HC595 DS: serial data input SC: shift clock. A low-to-high transition on this pin causes the data at the serial input pin to be shifted into the 8-bit shift register. Reset: A low on this pin resets the shift register portion of this device. LC: latch clock. A low-to-high transition on this pin loads the contents of the shift register into the output latch. OE: output enable. A low on this pin allows the data from the latches to be presented at the outputs. QA to QH: tri-state latch output SQH: the output of the eight stage of the shift register

27. Applications of the HC595 (1 of 2) The HC595 is often used to add parallel ports to the microcontroller. Both the connection methods shown in Figure 10.9 and 10.10 can be used to add parallel ports to the MCU.

28. Applications of the HC595 (2 of 2) Example 10.5 Describe how to use two 74HC595s to drive eight common cathode seven-segment displays assuming that the E clock frequency of the HCS12 is 24 MHz. Solution: Use the circuit in figure 10.12 to connect two 74HC595s to the HCS12.

29. #include “c:\miniide\hcs12.inc" org$1000 icntds.b1; loop count org$1500 lds#$1500; set up stack pointer bsetDDRK,$80; configure the PK7 pin for output jsropenspi0; configure SPI0 foreverldx#dispTab; use X as a pointer to the table movb#8,icnt; set loop count to 8 loopldaa1,x+; send the digit select byte to the 74HC595 jsrputcspi0; " ldaa1,x+; send segment pattern to 74HC595 jsrputcspi0; " bclrPTK,BIT7; transfer data from shift register to output bsetPTK,BIT7; latch ldy#1; display the digit for one ms jsrdelayby1ms; " decicnt; bneloop; if not reach digit 1, then next braforever; start from the start of the table Program to display 87654321 on display #7 to #0

30. openspi0movb#0,SPI0BR; set baud rate to 12 MHz movb#$50,SPI0CR1; disable interrupt, enable SPI, SCK idle low, ; latch data on rising edge, transfer data msb first movb#$02,SPI0CR2; disable bidirectional mode, stop SPI in wait mode movb#0,WOMS; enable Port S pull-up rts #include "c:\miniide\delay.asm" #include "c:\miniide\spi0util.asm" ; ******************************************************************** ; Each digit consists of two bytes of data. The first byte is ; digit select, the second byte is the digit pattern. ; ******************************************************************** dispTabdc.b$80,$7F,$40,$70,$20,$5F,$10,$5B dc.b$08,$33,$04,$79,$02,$6D,$01,$30 end

31. #include “c:\egnu091\include\hcs12.h” #include “c:\egnu091\include\spi0util.c” #include “c:\egnu091\include\delay.c” void openspi0(void); void main (void) { unsigned char disp_tab[8][2] = {{0x80,0x7F},{0x40,0x70},{0x20,0x5F},{0x10,0x5B}, {0x08,0x33},{0x04,0x79},{0x02,0x6D},{0x01,0x30}}; char i; openspi0(); /* configure the SPI0 module */ DDRK |= BIT7; /* configure pin PK7 as output */ while(1) { for (i = 0; i < 8; i++) { putcspi0(disp_tab[i][0]); /* send out digit select value */ putcspi0(disp_tab[i][1]); /* send out segment pattern */ PTK &= ~BIT7; /* transfer values to latches of 74HC595s */ PTK |= BIT7; /* " */ delayby1ms(1); /* display a digit for 1 ms */ }

32. The TC72 Digital Thermometer 10-bit resolution and SPI interface Pin assignment and block diagram shown in Figure 10.13. Capable of reading temperature from -55oC to 125oC. Can be used in continuous temperature conversion or one-shot conversion mode. Has internal clock generator to control the automatic temperature conversion sequence

33. Temperature Data Format Temperature is represented by a 10-bit two’s complement word with a resolution of 0.25oC per least significant bit. The converter is scaled from -128oC to +127oC with 0oC represented as 0x0000. The temperature value is stored in two 8-bit registers. Whenever the most significant bit is 1, the temperature is negative. A sample of temperature reading is shown.

34. TC72’s Serial Interface The CE input to the TC72 must be asserted (high) to enable SPI transfer. Data can be shifted on the rising edge or the falling edge depending on the idle polarity of the SCK source. Data transfer to and from the TC72 consists of one address byte followed by one or multiple data (2 to 4) bytes. The TC72 registers and their addresses are shown in Table 10.4. The most significant bit of the address byte determines whether a read (A7 = 0) or a write (A7 = 1) operation will occur. A multiple byte read operation will start from high address toward lower addresses. The user can send in the temperature result high byte address and read the temperature result high byte, low byte, and the control registers.

35. Procedure for Reading Temperature (1 of 2) Step 1 –Pull the CE pin high to enable SPI transfer. Step 2 –Send the temperature result high byte read address (0x02) to the TC72. Wait until the SPI transfer is complete. Step 3 –Read the temperature result high byte. The user needs to write a dummy byte into the SPI data register to trigger eight clock pulses. Step 4 –Read the temperature result low byte. Again, the user needs to write a dummy byte into the SPI data register to trigger eight clock pulses. Step 5 –Pull CE pin to low so that a new transfer can be started. Single-byte read and multiple-byte read timing diagrams are shown in Figures 10.15b and 10.15c.

36. Procedure for Reading Temperature (2 of 2)

37. Control Register The control register is used to select the shutdown, continuous, or one-shot conversion operating mode. The temperature conversion mode selection logic is shown in Table 10.5. At power up, the SHDN bit is 1. Thus the TC72 is in the shutdown mode. If the SHDN bit is 0, the TC72 will perform a temperature conversion approximately every 150 ms. A temperature conversion will be initiated by a write operation into the control register to select the continuous mode or one-shot mode. A typical circuit connection between the TC72 and the HCS12 is shown in Figure 10.16.

38. Example 10.6 Write a C program to read the temperature every 200 ms. Convert the temperature to a string so that it can be displayed in an appropriate output device. A pointer to hold the string will be passed to this function. The bus clock is 24 MHz.

39. #include “c:\egnu091\include\hcs12.h” #include “c:\egnu091\include\spi0util.c” #include “c:\egnu091\include\delay.c” #include “c:\egnu091\include\convert.c” void read_temp (char *ptr); void openspi0(void); char buf[10]; void main (void) { DDRM |= BIT1; /* configure the PM1 pin for output */ openspi0(); /* configure SPI0 module */ read_temp(&buf[0]); } void openspi0(void) { SPI0BR = 0x10; /* set baud rate to 6 MHz */ SPI0CR1 = 0x50;/* enable SPI0 to master mode, select rising edge to shift data in and out */ SPI0CR2 = 0x02;/* select normal mode and stop SPI in wait mode */ WOMS = 0x00; /* enable Port S pull-up */ }

40. void read_temp (char *ptr) { char hi_byte, lo_byte, temp, *bptr; unsigned int result; bptr = ptr; PTM |= BIT1; /* enable TC72 data transfer */ putcspi0(0x80); /* send out TC72 control register write address */ putcspi0(0x11); /* perform one shot conversion */ PTM &= ~BIT1; /* disable TC72 data transfer */ delayby100ms(2);/* wait until temperature conversion is complete */ PTM|= BIT1; /* enable TC72 data transfer */ putcspi0(0x02);/* send MSB temperature read address */ hi_byte = getcspi0();/* read the temperature high byte */ lo_byte = getcspi0(); /* save temperature low byte and clear SPIF */ PTM &= ~BIT1;/* disable TC72 data transfer */ lo_byte &= 0xC0; /* make sure the lower 6 bits are 0s */ result = (int) hi_byte * 256 + (int) lo_byte; if (hi_byte & 0x80) { /* temperature is negative */ result = ~result + 1; /* take the two' complement of result */ result >>= 6;

41. temp = result & 0x0003; /* place the lowest two bits in temp */ result>>= 2; /* get rid of fractional part */ *ptr++ = 0x2D; /* store the minus sign */ int2alpha(result, ptr); } else { /* temperature is positive */ result >>= 6; temp = result & 0x0003;/* save fractional part */ result >>= 2;/* get rid of fractional part */ int2alpha(result, ptr); /* convert to ASCII string */ } while(*bptr){ /* search the end of the string */ bptr++; }; switch (temp){/* add fractional digits to the temperature */ case 0: break; case 1:/* fractional part is.25 */ *bptr++ = 0x2E;/* add decimal point */ *bptr++ = 0x32; *bptr++ = 0x35; *bptr = '\0'; break;

42. case 2:/* fractional part is.5 */ *bptr++ = 0x2E;/* add decimal point */ *bptr++ = 0x35; *bptr = '\0'; break; case 3:/* fractional part is.75 */ *bptr++ = 0x2E;/* add decimal point */ *bptr++ = 0x37; *bptr++ = 0x35; *bptr = '\0'; break; default: break; }

43. The D/A Converter TLV5616 The TLV5616 is a 12-bit voltage output digital-to-analog converter (DAC) with SPI interface. The TLV5616 has an output settling time of 3 ms in fast mode and 9 ms in slow mode. A D/A conversion is started by writing a 16-bit serial string that contains 4 control bits and 12 data bits to the TLV5616. TLV5616 can operate from 2.7V to 5.5V.

44. TLV5616 Signal Pins AGND: analog ground CS:chip select (active low) DIN:serial data input FS:frame sync OUT:DAC analog output REFIN:reference analog input voltage SCLK:serial clock input VDD:positive power supply

45. Date Format -A 16-bit frame with 4 control bits and 12 data bits.

46. TLV5616 Output Voltage The output voltage is given by the following expression: –V OUT = 2  REF  code  2 n The reference voltage input cannot be higher than V DD /2.

47. Data Shifting Timing The FS pulse must be generated before data shifting can start. The highest data shift rate is 20 MHz.

48. CS and FS Trigger Sequence Pull FS to high. Pull CS to low. Pull FS to low. Send out control and data bits using the SPI transfer. Wait until all 16 bits have been shifted out; pull FS to high. Pull CS to high.

49. Circuit Connection between the TLV5616 and HCS12

50. Example 10.9 Write a program to generate a waveform that is a repetition of the waveform shown in Figure 10.21 using the circuit shown in Figure 10.20. The values to be sent to the TLV5616 to generate 0V, 1V, 2V, and 3V outputs are: val(0) = 0 val(1) = 2 12 /4 = 1024 val(2) = 2  2 12 /4 = 2048 val(3) = 3  2 12 /4 = 3072 The 16-bit values (in fast mode) to be written to the TLV5616 for this four voltages are as follows: code (0) = $4000 code (1) = $4400 code (2) = $4800 code (3) = $4C00

51. #include "c:\miniide\hcs12.inc" PM7equBIT7 PM6equBIT6 prologmacro bsetPTM,PM7; pull FS to high bclrPTM,PM6; pull CS to low bclrPTM,PM7; pull FS to low endm epilogmacro bsetPTM,PM7; pull FS to high bsetPTM,PM6; pull CS to high endm org$1500 lds#$1500; set up the stack pointer bsetDDRM,$C0; configure the PM6 and PM7 pins for output jsropenspi0; configure SPI0 properly foreverldx#D2ATab; Use X to point to the table ldab#8; entry count set to 8 iloopprolog; activate an FS pulse and pull CS to low ldaa1,x+; output 0V from OUT pin

52. jsrputcspi0;" ldaa1,x+;" jsrputcspi0;" epilog; pull PM7 and PM6 to high ldy#1; wait for 1 ms jsrdelayby1ms;" dbneb,iloop; reach the end of the table? braforever; yes, start from the beginning D2ATabdc.b$40,$00,$44,$00,$48,$00,$44,$00 dc.b$48,$00,$44,$00,$48,$00,$4C,$00 openspi0movb#0,SPI0BR; set baud rate to 12 MHz movb#$54,SPI0CR1 movb#$02,SPI0CR2 movb#0,WOMS; enable Port S pull-up rts #include "c:\miniide\delay.asm" #include "c:\miniide\spi0util.asm" end

53. Matrix LED Displays Many organizations have the need to display important information at the entrance or some corners of their buildings. The information to be displayed can be rotated. Common matrix LED displays format are 5  7, 5  8, and 8  8. One can find color matrix LEDs with red, green, and red color. Matrix LED displays can be organized as cathode-row or anode-row. All LEDs in a cathode-row matrix LED display have a common cathode whereas those in anode-row matrix LED display have a common anode.

56. The Driving Method of Matrix LED Displays Two parallel ports are needed to drive the matrix display. One port drives the column whereas the other port drives the rows. One needs to scan the matrix LED displays one row at a time, from top to bottom. For multiple matrix LED displays in the application, time- multiplexing technique needs to be used. Dedicated driver chips such as MAX6952 (SPI interface) and MAX6953 (I 2 C interface) are available for cathode- row matrix LED displays to simplify the interfacing.

57. The MAX6952 Matrix Display Driver Designed to drive cathode-row matrix displays with 5  7 organization Can operate with power supply from 2.7 V to 5.5 V Can drive four monocolor or two bicolor cathode-row matrix displays Has built-in 104-character Arial font and 24 user definable characters Allows automatic blinking control for each segment and provides 16-step digital brightness control Pin functions shown in Table 10.7 Pin connections illustrated in Table 10.8 and 10.9

60. One MAX6952 Drives Four Matrix Displays

61. Concatenation of Multiple MAX6952s Multiple MAX6952s can be concatenated to drive more than four matrix displays.

62. MAX6952 Block Diagram

63. Procedure for Writing the MAX6952 Step 1 –Pull the CLK signal to low. Step 2 –Pull the CS signal to low to enable the internal 16-bit shift register. Step 3 –Shift in 16 bits of data from the DIN pin with the most significant bit first. The most significant bit (D15) must be low for a write operation. Step 4 –Pull the CS signal to high. Step 5 –Pull the CLK to low.

64. Procedure for Reading the MAX6952 Register Step 1 –Pull the CLK signal to low. Step 2 –Pull the CS signal to low to enable SPI transfer. Step 3 –Clock 16 bits into the DIN pin with bit 15 first. Bit 15 must be a 1. Bits 14 to 8 contain the address of the register to be read. Bits 7 to 0 contain dummy data. Step 4 –Pull the CS signal to high. Bits 7 to of the shift register will be loaded with the data in the register addressed by bits 15 through 8. Step 5 –Pull CLK to low. Step 6 –Issue another read command and examine the bit stream at the DOUT pin. The second 8 bits are the contents of the register addressed by bits 14 to 8 in Step 3.

65. MAX6952 Register Map

66. Digit Registers (1 of 2) The MAX6952 uses eight digit registers to store the characters that the user wishes to display on the four 5  7 digits. These digit registers are placed in two planes (P0 and P1) with each plane having 4 bytes. Each LED digit is represented by 2 bytes of memory, one byte in plane P0 and the other in plane P1. A digit data can be updated in P0, or P1, or both at the same time as shown in Table 10.10. If the blink function is disabled, then the digit register data in plane P0 is used to multiplex the display. If the blink function is enabled, then the digit register data in both plane P0 and P1 are alternately used to multiplex the display. Blinking is achieved by multiplexing the LED display using data planes P0 and P1 on alternate phases of the blink clock. The multiplexing pattern in shown in Table 10.11.

67. Digit Registers (2 of 2) The data in the digit registers does not control the digit segments directly. The register data is used to address a character generator, which stores the data of a 128-character font. The lower 7 bits of he display data select the character font. The bit 7 of the register data selects whether the font data is used directly (D7 = 0) or whether the font is inverted (D7 = 1).

68. Configuration Register The configuration register is used to enter and exit shutdown, select the blink rate, enable and disable the blink function, clear the digit data, and reset the blink timing.

69. Intensity Registers Display brightness is controlled by four pulse-width modulators, one for each display digit. The upper four bits of the Intensity10 register control the intensity of the matrix display 1, whereas the lower four bits of the same register control the brightness of the display 0. Matrix display digits 3 and 2 are controlled by the upper four bits and lower four bits of the Intensity32 register, respectively. The modulator scales the average segment current in 16 steps from a maximum of 15/16 down to 1/16 of the peak current.

70. Scan Limit Register This register allows the user to choose between displaying two or four matrix displays. The multiplexing scheme drives digits 0 and 1 at the same time, then digits 2 and 3 at the same time.

71. Scan Test Register This register switches the drivers between two modes: normal and test. Display test mode turns on all LEDs by overriding, but not altering all control and digit registers. In display test mode, eight digits are scanned and the duty cycle is 7/16 (half power).

72. Character Generator Font Mapping The character generator comprises 104 characters in ROM, and 24 user-definable characters.` The lower 7 bits of the digit register select the character fonts. The character map follows the Arial font for 96 characters in the range from %0101000 to %1111111. The first 32 characters map the 24 user-defined positions (RAM00 to RAM23), plus eight extra common characters in ROM. When the msb is 0 the device will display the font normally. Otherwise, the chip will display the font inversely.

73. User-Defined Font Register The 24 user-definable characters are represented by 120 entries of 7-bit data, five entries per character in the SRAM. The 120 user definable font data are written and read through a single register at the address 0x05. An auto-incrementing font address pointer indirectly accesses the font data. The font data is written to and read from the MAX6952 indirectly, using the font address pointer. To define user fonts, the user first needs to set the font address pointer. This is done by placing the address in the font address pointer register and set the bit 7 to 1. After this, one can write the font data to the lower 7 bits and clear the bit 7. The font address pointer autoincrements after a valid access to the user-defined font data. The memory mapping of user-defined font register 0x05 is detailed in Table 10.12. The behavior of the font pointer address is illustrated in Table 10.13. To display the user-defined fonts, one must send in the RAM address from 0x00 to 0x17, corresponding to the font address pointer value that is 5  RAM address.

75. Blinking Operation The blinking operation makes the LED drivers flip between displaying the digit register data in planes P0 and P1. If the digit register data for any digit is different in two planes, then that digit appears to flip between two characters. To make a character to appear to blink on and off, write the character to one plane and use the blank character for the other plane. Blinking is enabled by setting the E bit of the configuration register. The blink speed can be programmed to be fast or slow and is determined by the frequency of the multiplex clock, OSC, and by setting the B bit of the configuration register.

76. Choosing Values for R SET and C SET The MAX6952 uses an RC oscillator to generate clock signals for display multiplexing. The recommended R SET and C SET values are 53.6K  and 26 pF, respectively. The recommended values for R SET and C SET will set the slow and fast blinking frequencies to 0.5 Hz and 1 Hz. The recommended values for R SET and C SET will set the peak current to 40 mA.

77. The Circuit that Daisy-Chains Two MAX6952 (1 of 2) Example 10.10 Connect eight matrix displays to these MAX6952 driver chips. Assume that the E clock frequency is 24 MHz. Write a program to configure the SPI function to shift data at 12 MHz and display the string “MSU ECET”.

78. The Circuit that Daisy-Chains Two MAX6952 (2 of 2) Solution: The SPI0 module should be configured with the following setting: –12 MHz baud rate –Master mode with interrupts disabled –Shift data on the rising edge with clock idle low –Shift data out most significant bit first –Disable mode fault –Stop SPI0 in wait mode The setting of two MAX6952s are as follows: –Intensity10 registers Set to maximum intensity Send the values 0x01, 0xFF, 0x01, and 0xFF to these two registers. –Intensity32 registers Set to maximum intensity Send the values 0x02, 0xFF, 0x02, and 0xFF to these two registers –Scan limit registers Drive four monocolor matrix displays Send the values 0x03, 0x01, 0x03, and 0x01 to these two registers

79. Configuration Registers Select P1 blink phase Not to clear digit data on both plane P1 and P0 Reset blink counter on the rising edge of CS Disable blink function Select slow blinking (doesn’t matter) Select normal mode Send the values 0x04, 0x11, 0x04, and 0x11 to these two registers

80. Display Test Registers Disable test. Send the values 0x07, 0x00, 0x07, and 0x00 to these two registers.

81. Digit 0 Registers (Rightmost Digit) Plane P0 Display space character and letter T on he display 0 of the first and second MAX6952. Send the values 0x20, 0x54, 0x20, and 0x20 to these two registers.

82. Digit 1 registers (second rightmost digit) Plane P0 Display letter U and E on the display 1 of the 1st and 2nd MAX6952. Send the values 0x21, 0x45, 0x21, and 0x55 to these two registers.

83. Digit 2 Registers (Second Leftmost Digit) Plane 0 Display letters S and C on the display 2 of the 1st and 2nd MAX6952. Send the values 0x22, 0x43, 0x22, and 0x53 to these registers.

84. #include “c:\egnu091\include\hcs12.h” #include “c:\egnu091\include\spi0util.c” void sendtomax(char x1, char x2, char x3, char x4); void openspi0(void); void main (void) { openspi0(); DDRM |= BIT5; // configure PM5 pin for output sendtomax(0x01, 0xFF, 0x01, 0xFF); // set intensity for digits 0 & 1 sendtomax(0x02, 0xFF, 0x02, 0xFF); // set intensity for digits 2 & 3 sendtomax(0x03, 0x01, 0x03, 0x01); // set scan limit to drive 4 digits sendtomax(0x04, 0x11, 0x04, 0x11); // set configuration register sendtomax(0x07, 0x00, 0x07, 0x00); // disable test Digit 3 Registers (Leftmost Digit) Plane 0 Display letters M and E on the display 3 of the 1st and 2nd MAX6952. Send the values 0x23, 0x45, 0x23, and 0x4D to these registers. –The program that perform the desired configuration is as follows:

85. sendtomax(0x20, 0x54, 0x20, 0x20); // value for digit 0 sendtomax(0x21, 0x45, 0x21, 0x55); // value for digit 1 sendtomax(0x22, 0x43, 0x22, 0x53); // value for digit 2 sendtomax(0x23, 0x45, 0x23, 0x4D); // value for digit 3 } void sendtomax (char c1, char c2, char c3, char c4) { char temp; PTM &= ~BIT5; /* enable SPI transfer to MAX6952 */ putcspi0(c1);/* send c1 to MAX6952 */ putcspi0(c2); /* send c2 to MAX6952 */ putcspi0(c3); /* send c3 to MAX6952 */ putcspi0(c4); /* send c4 to MAX6952 */ PTM |= BIT5;/* load data from shift register to latch */ } void openspi0(void) { SPI0BR = 0x00; /* set baud rate to 12 MHz */ SPI0CR1= 0x50; /* disable interrupt, set master mode, shift data on rising edge, clock idle low */ SPI0CR2= 0x02; /* disable mode fault, disable SPI in wait mode */ WOMS = 0; /* enable Port S pull-up */ }

86. void main (void) { openspi0(); DDRM |= BIT5; // configure PM5 pin for output sendtomax(0x01, 0xFF, 0x01, 0xFF); sendtomax(0x02, 0xFF, 0x02, 0xFF); sendtomax(0x03, 0x01, 0x03, 0x01); sendtomax(0x04, 0x19, 0x04, 0x19); // configuration register, blink at phase P1 sendtomax(0x07, 0x00, 0x07, 0x00); // disable test sendtomax(0x20, 0x54, 0x20, 0x20); // value for digit 0 on plane P0 sendtomax(0x21, 0x45, 0x21, 0x55); // value for digit 1 sendtomax(0x22, 0x43, 0x22, 0x53); // value for digit 2 sendtomax(0x23, 0x45, 0x23, 0x4D); // value for digit 3 sendtomax(0x40, 0x20, 0x40, 0x20); // value for digit 0 on plane P1 (space) sendtomax(0x41, 0x20, 0x41, 0x20); // value for digit 1 “ sendtomax(0x42, 0x20, 0x42, 0x20); // value for digit 2“ sendtomax(0x43, 0x20, 0x43, 0x20); // value for digit 3“ } Example 10.11 Modify the previous example to blink the display at a slow rate. Solution: The setting of the configuration needs to be changed and we need to send the space character (0x20) to the plane P1. Send the values 0x04, 0x19, 0x03, and 0x19 to the configuration registers.

87. #include “c:\egnu091\include\hcs12.h” #include “c:\egnu091\include\spi0util.c” #include “c:\egnu091\include\delay.c” void send2max (char x1, char x2, char x3, char x4); void openspi0 (void); char msgP0[41] = "08:30:40 Wednesday, 72 o F, humidity: 60% "; Example 10.12 For the circuit shown in Figure 10.30, write a program to display the following message and shift the information from right-to-left every second and enable blinking: 08:30:40 Wednesday, 72oF, humidity: 60% Solution: One possible solution is as follows: –Use the plane P0 to shift the message once every half a second. –Use the message in plane P0 to multiplex the displays in half a second. –Use the message sent to the plane P1 to multiplex the displays in the next half of a second. –Display space characters in plane P1 only to create blinking effect. –Use a delay function to control the shifting of the message.

88. void main (void) { char i1, i2, i3, i4; char j1, j2, j3, j4; char k; openspi0(); DDRM |= BIT5; // configure PM5 pin for output send2max(0x01, 0xFF, 0x01, 0xFF); send2max(0x02, 0xFF, 0x02, 0xFF); send2max(0x03, 0x01, 0x03, 0x01); send2max(0x04, 0x1D, 0x04, 0x1D); // configuration register send2max(0x40, 0x20, 0x40, 0x20); // send space character to plane P1 send2max(0x41, 0x20, 0x41, 0x20); send2max(0x42, 0x20, 0x42, 0x20); send2max(0x43, 0x20, 0x43, 0x20); k = 0; while (1) { i1 = k; i2 = (k+1)%40; i3 = (k+2)%40; i4 = (k+3)%40;

89. j1 = (k+4)%40; j2 = (k+5)%40; j3 = (k+6)%40; j4 = (k+7)%40; sendtomax(0x20, msgP0[i1], 0x20, msgP0[j1]); sendtomax(0x21, msgP0[i2], 0x21, msgP0[j2]); sendtomax(0x22, msgP0[i3], 0x22, msgP0[j3]); sendtomax(0x23, msgP0[i4], 0x23, msgP0[j4]); delayby100ms(10); /* wait for 1 s */ k = (k+1)%40; } void sendtomax (char c1, char c2, char c3, char c4) { PTM &= ~BIT5; /* enable SPI transfer to MAX6952 */ putcspi0(c1);/* send c1 to MAX6952 */ putcspi0(c2); /* send c2 to MAX6952 */ putcspi0(c3); /* send c3 to MAX6952 */ putcspi0(c4); /* send c4 to MAX6952 */ PTM |= BIT5;/* load data from shift register to latch */ }

90. Example 10.13 Write a program to define fonts for three special characters as shown below. Store these three special characters’ font at locations from 0x00 to 0x0E of the MAX6952.

91. #include “c:\egnu091\include\hcs12.h” #include “c:\egnu091\include\spi0util.c” char fonts [15] = {0x70,0x40,0x7F,0x40,0x70,0x48,0x38,0x0F,0x38,0x48,0x49, 0x49,0x7F,0x49,0x49}; void send_font (char xc); void openspi0 (void); void main (void) { char i; DDRM |= BIT5; /* configure PM5 pin for output */ openspi0();/* configure SPI module properly */ send_font(0x80); /* set font address pointer address to 0x00 */ for (i = 0; i < 15; i++) send_font(fonts[i]); } void send_font(char xx) { PTM &= ~BIT5; /* enable SPI transfer */ putcspi0(0x05);/* specify font address pointer */ putcspi0(xx); /* send a font value */ PTM |= BIT5;/* load data in shift register to destination */ }

92. void openspi0(void) { SPI0BR = 0x00; /* set baud rate to 12 MHz */ SPI0CR1= 0x50; /* disable interrupt, set master mode, shift data on rising edge, clock idle low */ SPI0CR2 = 0x02; /* disable mode fault, disable SPI in wait mode */ WOMS = 0; /* enable Port S pull-up */ } The statements to display those three Chinese characters followed by letters A, B, C, D, and E from left to right on the matrix LED displays shown in Figure 10.30 are as follows: sendtomax(0x20, 0x42, 0x20, 0x00); // 0x00 is the address of the first character font sendtomax(0x21, 0x43, 0x21, 0x01); // 0x01 is the address of the second character font sendtomax(0x22, 0x44, 0x22, 0x02); // 0x02 is the address of the third character font sendtomax(0x23, 0x45, 0x23, 0x41);