Programming the 8051 Microcontroller Dr. Konstantinos Tatas

Programming the 8051 Microcontroller Dr. Konstantinos Tatas
Lecture 3 Programming the 8051 Microcontroller Dr. Konstantinos Tatas

A B R0 R1 R3 R4 R2 R5 R7 R6 DPH DPL PC DPTR Some bit Register Some 8-bit Registers of the 8051 A: Accumulator B: Used specially in MUL/DIV R0-R7: GPRs Registers ACOE343 - Embedded Real-Time Processor Systems - Frederick University

8051 Programming using Assembly

The MOV Instruction – Addressing Modes
MOV dest,source ; dest = source MOV A,#72H ;A=72H MOV A, #’r’ ;A=‘r’ OR 72H MOV R4,#62H ;R4=62H MOV B,0F9H ;B=the content of F9’th byte of RAM MOV DPTR,#7634H MOV DPL,#34H MOV DPH,#76H MOV P1,A ;mov A to port 1 Note 1: MOV A,#72H ≠ MOV A,72H After instruction “MOV A,72H ” the content of 72’th byte of RAM will replace in Accumulator. MOV AL,72H MOV A,#72H MOV AL,’r’ MOV A,#’r’ MOV BX,72H MOV AL,[BX] MOV A,72H Note 2: MOV A,R3 ≡ MOV A,3 ACOE343 - Embedded Real-Time Processor Systems - Frederick University

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Arithmetic Instructions ADD A, Source ;A=A+SOURCE ADD A,#6 ;A=A+6 ADD A,R6 ;A=A+R6 ADD A,6 ;A=A+[6] or A=A+R6 ADD A,0F3H ;A=A+[0F3H] ACOE343 - Embedded Real-Time Processor Systems - Frederick University

Set and Clear Instructions
SETB bit ; bit=1 CLR bit ; bit=0 SETB C ; CY=1 SETB P0.0 ;bit 0 from port 0 =1 SETB P3.7 ;bit 7 from port 3 =1 SETB ACC.2 ;bit 2 from ACCUMULATOR =1 SETB 05 ;set high D5 of RAM loc. 20h Note: CLR instruction is as same as SETB i.e: CLR C ;CY=0 But following instruction is only for CLR: CLR A ;A=0 ACOE343 - Embedded Real-Time Processor Systems - Frederick University

SUBB A,source ;A=A-source-CY SETB C ;CY=1 SUBB A,R5 ;A=A-R5-1 ADC A,source ;A=A+source+CY ADC A,R5 ;A=A+R5+1 ACOE343 - Embedded Real-Time Processor Systems - Frederick University

DEC byte ;byte=byte-1 INC byte ;byte=byte+1 INC R7 DEC A DEC 40H ; [40]=[40]-1 CPL A ;1’s complement Example: MOV A,#55H ;A= B L01: CPL A MOV P1,A ACALL DELAY SJMP L01 NOP & RET & RETI All are like 8086 instructions.  CALL ACOE343 - Embedded Real-Time Processor Systems - Frederick University

Logic Instructions ANL byte/bit ORL byte/bit XRL byte EXAMPLE: MOV R5,#89H ANL R5,#08H ACOE343 - Embedded Real-Time Processor Systems - Frederick University

Rotate Instructions RR A Accumulator rotate right RL A Accumulator Rotate left RRC A Accumulator Rotate right through the carry. RLC A Accumulator Rotate left through the carry. ACOE343 - Embedded Real-Time Processor Systems - Frederick University

Structure of Assembly language and Running an 8051 program
EDITOR PROGRAM ASSEMBLER LINKER OH Myfile.asm Myfile.obj Other obj file Myfile.lst Myfile.abs Myfile.hex ORG 0H MOV R5,#25H MOV R7,#34H MOV A,#0 ADD A,R5 ADD A,#12H HERE: SJMP HERE END ACOE343 - Embedded Real-Time Processor Systems - Frederick University

Memory mapping in 8051 ROM memory map in 8051 family 0000H 0FFFH 1FFFH 7FFFH 8751 AT89C51 8752 AT89C52 4k 8k 32k DS from Atmel Corporation from Dallas Semiconductor ACOE343 - Embedded Real-Time Processor Systems - Frederick University

RAM memory space allocation in the 8051 7FH 30H 2FH 20H 1FH 17H 10H 0FH 07H 08H 18H 00H Register Bank 0 (Stack) Register Bank 1 Register Bank 2 Register Bank 3 Bit-Addressable RAM Scratch pad RAM ACOE343 - Embedded Real-Time Processor Systems - Frederick University

8051 Flag bits and the PSW register
CY AC F0 RS1 OV RS0 P -- CY PSW.7 Carry flag AC PSW.6 Auxiliary carry flag -- PSW.5 Available to the user for general purpose RS1 PSW.4 Register Bank selector bit 1 RS0 PSW.3 Register Bank selector bit 0 OV PSW.2 Overflow flag -- PSW.1 User define bit P PSW.0 Parity flag Set/Reset odd/even parity RS1 RS0 Register Bank Address H-07H H-0FH H-17H H-1FH ACOE343 - Embedded Real-Time Processor Systems - Frederick University

Instructions that Affect Flag Bits: Note: X can be 0 or 1 ACOE343 - Embedded Real-Time Processor Systems - Frederick University

Example: MOV A,#88H ADD A,#93H 11B CY=1 AC=0 P=0 Example: MOV A,#9CH ADD A,#64H 9C CY=1 AC=1 P=0 Example: MOV A,#38H ADD A,#2FH +2F CY=0 AC=1 P=1 ACOE343 - Embedded Real-Time Processor Systems - Frederick University

Addressing Modes Immediate Register Direct Register Indirect Indexed ACOE343 - Embedded Real-Time Processor Systems - Frederick University

Immediate Addressing Mode
MOV A,#65H MOV A,#’A’ MOV R6,#65H MOV DPTR,#2343H MOV P1,#65H Example : Num EQU 30 … MOV R0,Num MOV DPTR,#data1 ORG 100H data1: db “Example” ACOE343 - Embedded Real-Time Processor Systems - Frederick University

Example Write the decimal value 4 on the SSD in the following figure. Switch the decimal point off. ACOE343 - Embedded Real-Time Processor Systems - Frederick University

Register Addressing Mode
MOV Rn, A ;n=0,..,7 ADD A, Rn MOV DPL, R6 MOV DPTR, A MOV Rm, Rn ACOE343 - Embedded Real-Time Processor Systems - Frederick University

Direct Addressing Mode
Although the entire of 128 bytes of RAM can be accessed using direct addressing mode, it is most often used to access RAM loc. 30 – 7FH. MOV R0, 40H MOV 56H, A MOV A, 4 ; ≡ MOV A, R4 MOV 6, 2 ; copy R2 to R6 ; MOV R6,R2 is invalid ! SFR register and their address MOV 0E0H, #66H ; ≡ MOV A,#66H MOV 0F0H, R2 ; ≡ MOV B, R2 MOV 80H,A ; ≡ MOV P1,A ACOE343 - Embedded Real-Time Processor Systems - Frederick University

Register Indirect Addressing Mode
In this mode, register is used as a pointer to the data. MOV ; move content of RAM loc.Where address is held by Ri into A ( i=0 or 1 ) MOV @R1,B In other word, the content of register R0 or R1 is sources or target in MOV, ADD and SUBB insructions. Example: Write a program to copy a block of 10 bytes from RAM location sterting at 37h to RAM location starting at 59h. Solution: MOV R0,37h ; source pointer MOV R1,59h ; dest pointer MOV R2,10 ; counter L1: MOV MOV @R1,A INC R0 INC R1 DJNZ R2,L1 jump ACOE343 - Embedded Real-Time Processor Systems - Frederick University

Indexed Addressing Mode And On-Chip ROM Access
This mode is widely used in accessing data elements of look-up table entries located in the program (code) space ROM at the 8051 MOVC A= content of address A +DPTR from ROM Note: Because the data elements are stored in the program (code ) space ROM of the 8051, it uses the instruction MOVC instead of MOV. The “C” means code. ACOE343 - Embedded Real-Time Processor Systems - Frederick University

Example: Assuming that ROM space starting at 250h contains “Hello.”, write a program to transfer the bytes into RAM locations starting at 40h. Solution: ORG 0 MOV DPTR,#MYDATA MOV R0,#40H L1: CLR A MOVC JZ L2 MOV @R0,A INC DPTR INC R0 SJMP L1 L2: SJMP L2 ; ORG 250H MYDATA: DB “Hello”,0 END Notice the NULL character ,0, as end of string and how we use the JZ instruction to detect that. ACOE343 - Embedded Real-Time Processor Systems - Frederick University

Example: Write a program to get the x value from P1 and send x2 to P2, continuously . Solution: ORG 0 ;code segment MOV DPTR, #TAB1 ;moving data segment to data pointer MOV A,#0FFH ;configuring P1 as input port MOV P1,A L01: MOV A,P1 ;reading value from P1 MOVC MOV P2,A SJMP L01 ; ORG 300H ;data segment TAB1: DB 0,1,4,9,16,25,36,49,64,81 END ACOE343 - Embedded Real-Time Processor Systems - Frederick University

External Memory Addressing
MOVX ; A [R1] (in external memory) MOVX A ACOE343 - Embedded Real-Time Processor Systems - Frederick University

16-bit, BCD and Signed Arithmetic in 8051
Exercise: Write a program to add n 16-bit number. Get n from port 1. And sent Sum to SSD a) in hex b) in decimal Write a program to subtract P1 from P0 and send result to LCD (Assume that “ACAL DISP” display A to SSD ) ACOE343 - Embedded Real-Time Processor Systems - Frederick University

MUL & DIV MUL AB ;B|A = A*B MOV A,#25H MOV B,#65H MUL AB ;25H*65H=0E99 ;B=0EH, A=99H DIV AB ;A = A/B, B = A mod B MOV A,#25 MOV B,#10 DIV AB ;A=2, B=5 ACOE343 - Embedded Real-Time Processor Systems - Frederick University

Stack in the 8051 The register used to access the stack is called SP (stack pointer) register. The stack pointer in the 8051 is only 8 bits wide, which means that it can take value 00 to FFH. When 8051 powered up, the SP register contains value 07. 7FH 30H 2FH 20H 1FH 17H 10H 0FH 07H 08H 18H 00H Register Bank 0 (Stack) Register Bank 1 Register Bank 2 Register Bank 3 Bit-Addressable RAM Scratch pad RAM ACOE343 - Embedded Real-Time Processor Systems - Frederick University

Example: MOV R6,#25H MOV R1,#12H MOV R4,#0F3H PUSH 6 PUSH 1 PUSH 4 0BH 0AH 09H 08H Start SP=07H 25 0BH 0AH 09H 08H SP=08H 12 25 0BH 0AH 09H 08H SP=09H F3 12 25 0BH 0AH 09H 08H SP=10H ACOE343 - Embedded Real-Time Processor Systems - Frederick University

Example (cont.) POP 4 POP 1 POP 6 F3 12 25 0BH 0AH 09H 08H SP=10H 12 25 0BH 0AH 09H 08H SP=09H 25 0BH 0AH 09H 08H SP=08H 0BH 0AH 09H 08H Start SP=07H ACOE343 - Embedded Real-Time Processor Systems - Frederick University

How to use the stack You can use the stack as temporary storage for variables when calling functions RLC A ;you can only rotate A Call function DIV AB ; A has the wrong value!!!!! … function: MOV A, #5 ;values are for example sake MOV B, #10 MUL AB ;you can only multiply on A RET ACOE343 - Embedded Real-Time Processor Systems - Frederick University

Example (correct) RLC A ;you can only rotate A PUSH A ;saving A and B on the stack before PUSH B ;calling function Call function POP B ;restoring B POP A ;and A (POP in reverse order) DIV AB ; A has the correct value!!!!! … function: MOV A, #5 ;values are for example sake MOV B, #10 MUL AB ;you can only multiply on A RET ACOE343 - Embedded Real-Time Processor Systems - Frederick University

Saving PSW The Program Status Word registers contains flags that are often important for correct program flow You can push PSW on the stack before calling a function ADD A, R0 PUSH PSW PUSH A ;saving A and R0 on the stack before PUSH R0 ;calling function Call function POP R0 ;restoring R0 POP A ;and A (POP in reverse order) POP PSW JC loop ;If this means the carry from the ;function then don’t push PSW … function: MOV A, #5 ;values are for example sake ADD A, R2 ;the flags are set according to ADD result RET ACOE343 - Embedded Real-Time Processor Systems - Frederick University

LOOP and JUMP Instructions
DJNZ: Write a program to clear ACC, then add 3 to the accumulator ten times Solution: MOV A,#0; MOV R2,#10 AGAIN: ADD A,#03 DJNZ R2,AGAING ;repeat until R2=0 (10 times) MOV R5,A ACOE343 - Embedded Real-Time Processor Systems - Frederick University

Other conditional jumps : JZ Jump if A=0 JNZ Jump if A/=0 DJNZ Decrement and jump if A/=0 CJNE A,byte Jump if A/=byte CJNE reg,#data Jump if byte/=#data JC Jump if CY=1 JNC Jump if CY=0 JB Jump if bit=1 JNB Jump if bit=0 JBC Jump if bit=1 and clear bit ACOE343 - Embedded Real-Time Processor Systems - Frederick University

SJMP and LJMP: LJMP(long jump) LJMP is an unconditional jump. It is a 3-byte instruction in which the first byte is the opcode, and the second and third bytes represent the 16-bit address of the target location. The 20byte target address allows a jump to any memory location from 0000 to FFFFH. SJMP(short jump) In this 2-byte instruction. The first byte is the opcode and the second byte is the relative address of the target location. The relative address range of 00-FFH is divided into forward and backward jumps, that is , within -128 to +127 bytes of memory relative to the address of the current PC. ACOE343 - Embedded Real-Time Processor Systems - Frederick University

CJNE , JNC Exercise: Write a program that compare R0,R1. If R0>R1 then send 1 to port 2, else if R0<R1 then send 0FFh to port 2, else send 0 to port 2. ACOE343 - Embedded Real-Time Processor Systems - Frederick University

CALL Instructions Another control transfer instruction is the CALL instruction, which is used to call a subroutine. LCALL(long call) In this 3-byte instruction, the first byte is the opcode an the second and third bytes are used for the address of target subroutine. Therefore, LCALL can be used to call subroutines located anywhere within the 64K byte address space of the 8051. ACOE343 - Embedded Real-Time Processor Systems - Frederick University

ACALL (absolute call) ACALL is 2-byte instruction in contrast to LCALL, which is 13 bytes. Since ACALL is a 2-byte instruction, the target address of the subroutine must be within 2K bytes address because only 11 bits of the 2 bytes are used for the address. There is no difference between ACALL and LCALL in terms of saving the program counter on the stack or the function of the RET instruction. The only difference is that the target address for LCALL can be anywhere within the 64K byte address space of the 8051 while the target address of ACALL must be within a 2K-byte range. ACOE343 - Embedded Real-Time Processor Systems - Frederick University

Example A B R5 R7 Address Data ORG 0H VAL1 EQU 05H MOV R5,#25H LOOP: MOV R7,#VAL1 MOV A,#0 ADD A,R5 ADD A,#12H RRC A DJNZ A, LOOP SETB ACC.3 CLR A CJNE A, #0, LOOP HERE: SJMP HERE END ACOE343 - Embedded Real-Time Processor Systems - Frederick University

I/O Port Programming Port 1（pins 1-8）  Port 1 is denoted by P1. P1.0 ~ P1.7 We use P1 as examples to show the operations on ports. P1 as an output port (i.e., write CPU data to the external pin) P1 as an input port (i.e., read pin data into CPU bus) ACOE343 - Embedded Real-Time Processor Systems - Frederick University

A Pin of Port 1 D Q Clk Q Vcc Load(L1) Read latch Read pin Write to latch Internal CPU bus M1 P1.X pin P1.X TB1 TB2 P0.x 8051 IC ACOE343 - Embedded Real-Time Processor Systems - Frederick University

Hardware Structure of I/O Pin
Each pin of I/O ports Internal CPU bus：communicate with CPU A D latch store the value of this pin D latch is controlled by “Write to latch” Write to latch＝1：write data into the D latch 2 Tri-state buffer： TB1: controlled by “Read pin” Read pin＝1：really read the data present at the pin TB2: controlled by “Read latch” Read latch＝1：read value from internal latch A transistor M1 gate Gate=0: open Gate=1: close ACOE343 - Embedded Real-Time Processor Systems - Frederick University

Tri-state Buffer  Output Input Tri-state control (active high) L L H
Low Highimpedance (open-circuit) H H  ACOE343 - Embedded Real-Time Processor Systems - Frederick University

Writing “1” to Output Pin P1.X
D Q Clk Q Vcc Load(L1) Read latch Read pin Write to latch Internal CPU bus M1 P1.X pin P1.X TB2 2. output pin is Vcc 1. write a 1 to the pin 1 output 1 TB1 8051 IC ACOE343 - Embedded Real-Time Processor Systems - Frederick University

Writing “0” to Output Pin P1.X
D Q Clk Q Vcc Load(L1) Read latch Read pin Write to latch Internal CPU bus M1 P1.X pin P1.X TB2 2. output pin is ground 1. write a 0 to the pin output 0 1 TB1 8051 IC ACOE343 - Embedded Real-Time Processor Systems - Frederick University

Port 1 as Output（Write to a Port）
Send data to Port 1： MOV A,#55H BACK: MOV P1,A ACALL DELAY CPL A SJMP BACK Let P1 toggle. You can write to P1 directly. ACOE343 - Embedded Real-Time Processor Systems - Frederick University

Reading Input v.s. Port Latch
When reading ports, there are two possibilities： Read the status of the input pin. （from external pin value） MOV A, PX JNB P2.1, TARGET ; jump if P2.1 is not set JB P2.1, TARGET ; jump if P2.1 is set Figures C-11, C-12 Read the internal latch of the output port. ANL P1, A ; P1 ← P1 AND A ORL P1, A ; P1 ← P1 OR A INC P ; increase P1 Figure C-17 Table C-6 Read-Modify-Write Instruction (or Table 8-5) See Section 8.3 ACOE343 - Embedded Real-Time Processor Systems - Frederick University

Reading “High” at Input Pin
D Q Clk Q Vcc Load(L1) Read latch Read pin Write to latch Internal CPU bus M1 P1.X pin P1.X 2. MOV A,P1 external pin=High TB2 write a 1 to the pin MOV P1,#0FFH 1 1 TB1 3. Read pin=1 Read latch=0 Write to latch=1 8051 IC ACOE343 - Embedded Real-Time Processor Systems - Frederick University

Reading “Low” at Input Pin
D Q Clk Q Vcc Load(L1) Read latch Read pin Write to latch Internal CPU bus M1 P1.X pin P1.X 2. MOV A,P1 external pin=Low TB2 write a 1 to the pin MOV P1,#0FFH 1 TB1 3. Read pin=1 Read latch=0 Write to latch=1 8051 IC ACOE343 - Embedded Real-Time Processor Systems - Frederick University

Port 1 as Input（Read from Port）
In order to make P1 an input, the port must be programmed by writing 1 to all the bit. MOV A,#0FFH ;A= B MOV P1,A ;make P1 an input port BACK: MOV A,P ;get data from P0 MOV P2,A ;send data to P2 SJMP BACK To be an input port, P0, P1, P2 and P3 have similar methods. Program is to read data from P0 and then send data to P1 ACOE343 - Embedded Real-Time Processor Systems - Frederick University

Instructions For Reading an Input Port
Following are instructions for reading external pins of ports: Mnemonics Examples Description MOV A,PX MOV A,P2 Bring into A the data at P2 pins JNB PX.Y,.. JNB P2.1,TARGET Jump if pin P2.1 is low JB PX.Y,.. JB P1.3,TARGET Jump if pin P1.3 is high MOV C,PX.Y MOV C,P2.4 Copy status of pin P2.4 to CY ACOE343 - Embedded Real-Time Processor Systems - Frederick University

Reading Latch Exclusive-or the Port 1： MOV P1,#55H ;P1= ORL P1,#0F0H ;P1= 1. The read latch activates TB2 and bring the data from the Q latch into CPU. Read P1.0=0 2. CPU performs an operation. This data is ORed with bit 1 of register A. Get 1. 3. The latch is modified. D latch of P1.0 has value 1. 4. The result is written to the external pin. External pin (pin 1: P1.0) has value 1. ACOE343 - Embedded Real-Time Processor Systems - Frederick University

Reading the Latch D Q Clk Q
1. Read pin=0 Read latch=1 Write to latch=0 (Assume P1.X=0 initially) D Q Clk Q Vcc Load(L1) Read latch Read pin Write to latch Internal CPU bus M1 P1.X pin P1.X TB2 2. CPU compute P1.X OR 1 4. P1.X=1 1 1 3. write result to latch Read pin= Read latch= Write to latch=1 TB1 8051 IC ACOE343 - Embedded Real-Time Processor Systems - Frederick University

Read-modify-write Feature
Read-modify-write Instructions Table C-6 This features combines 3 actions in a single instruction： 1. CPU reads the latch of the port 2. CPU perform the operation 3. Modifying the latch 4. Writing to the pin Note that 8 pins of P1 work independently. ACOE343 - Embedded Real-Time Processor Systems - Frederick University

Port 1 as Input（Read from latch）
Exclusive-or the Port 1： MOV P1,#55H ;P1= AGAIN: XOR P1,#0FFH ;complement ACALL DELAY SJMP AGAIN Note that the XOR of 55H and FFH gives AAH. XOR of AAH and FFH gives 55H. The instruction read the data in the latch (not from the pin). The instruction result will put into the latch and the pin. ACOE343 - Embedded Real-Time Processor Systems - Frederick University

Read-Modify-Write Instructions
Mnemonics Example SETB P1.4 SETB PX.Y CLR P1.3 CLR PX.Y MOV P1.2,C MOV PX.Y,C DJNZ P1,TARGET DJNZ PX, TARGET INC P1 INC CPL P1.2 CPL JBC P1.1, TARGET JBC PX.Y, TARGET XRL P1,A XRL ORL P1,A ORL ANL P1,A ANL DEC P1 DEC ANL: Latch data AND with A , then save back to latch and write to the external pin ORL: OR XRL: XOR JBC: jump to TARGET if bit set and clear bit CPL: complement INC: increase DEC: decrease DJNZ: decrease P1 and jump if P1 not zero MOV the latch value to carry CLR: clear bit, SETB: set bit ACOE343 - Embedded Real-Time Processor Systems - Frederick University

You are able to answer this Questions:
How to write the data to a pin？ How to read the data from the pin？ Read the value present at the external pin. Why we need to set the pin first？ Read the value come from the latch（not from the external pin）. Why the instruction is called read-modify write? ACOE343 - Embedded Real-Time Processor Systems - Frederick University

Other Pins P1, P2, and P3 have internal pull-up resisters. P1, P2, and P3 are not open drain. P0 has no internal pull-up resistors and does not connects to Vcc inside the 8051. P0 is open drain. Compare the figures of P1.X and P0.X.  However, for a programmer, it is the same to program P0, P1, P2 and P3. All the ports upon RESET are configured as output. ACOE343 - Embedded Real-Time Processor Systems - Frederick University

A Pin of Port 0 D Q Clk Q Read latch Read pin Write to latch Internal CPU bus M1 P0.X pin P1.X TB1 TB2 P1.x 8051 IC ACOE343 - Embedded Real-Time Processor Systems - Frederick University

Port 0（pins 32-39） P0 is an open drain. Open drain is a term used for MOS chips in the same way that open collector is used for TTL chips.  When P0 is used for simple data I/O we must connect it to external pull-up resistors. Each pin of P0 must be connected externally to a 10K ohm pull-up resistor. With external pull-up resistors connected upon reset, port 0 is configured as an output port. Open drain is a term used for MOS chips in the same way that open collector is used for TTL chips. ACOE343 - Embedded Real-Time Processor Systems - Frederick University

Port 0 with Pull-Up Resistors
DS5000 8751 8951 Vcc 10 K Port 0 ACOE343 - Embedded Real-Time Processor Systems - Frederick University

Dual Role of Port 0 When connecting an 8051/8031 to an external memory, the 8051 uses ports to send addresses and read instructions. 8031 is capable of accessing 64K bytes of external memory. 16-bit address：P0 provides both address A0-A7, P2 provides address A8-A15. Also, P0 provides data lines D0-D7. When P0 is used for address/data multiplexing, it is connected to the 74LS373 to latch the address. There is no need for external pull-up resistors as shown in Chapter 14. ACOE343 - Embedded Real-Time Processor Systems - Frederick University

74LS373 D 74LS373 ALE P0.0 P0.7 PSEN A0 A7 D0 D7 P2.0 P2.7 A8 A15 OE OC EA G 8051 ROM ACOE343 - Embedded Real-Time Processor Systems - Frederick University

Reading ROM (1/2) latches the address and send to ROM 1. Send address to ROM D 74LS373 ALE P0.0 P0.7 PSEN A0 A7 D0 D7 P2.0 P2.7 A8 A12 OE OC EA G 8051 ROM Address ACOE343 - Embedded Real-Time Processor Systems - Frederick University

Reading ROM (2/2) latches the address and send to ROM D 74LS373 ALE P0.0 P0.7 PSEN A0 A7 D0 D7 P2.0 P2.7 A8 A12 OE OC EA G 8051 ROM Address 3. ROM send the instruction back ACOE343 - Embedded Real-Time Processor Systems - Frederick University

ALE Pin The ALE pin is used for de-multiplexing the address and data by connecting to the G pin of the 74LS373 latch. When ALE=0, P0 provides data D0-D7. When ALE=1, P0 provides address A0-A7. The reason is to allow P0 to multiplex address and data. ACOE343 - Embedded Real-Time Processor Systems - Frederick University

Port 2（pins 21-28） Port 2 does not need any pull-up resistors since it already has pull-up resistors internally. In an 8031-based system, P2 are used to provide address A8-A15. ACOE343 - Embedded Real-Time Processor Systems - Frederick University

Port 3（pins 10-17） Port 3 does not need any pull-up resistors since it already has pull-up resistors internally. Although port 3 is configured as an output port upon reset, this is not the way it is most commonly used. Port 3 has the additional function of providing signals. Serial communications signal：RxD, TxD（Chapter 10） External interrupt：/INT0, /INT1（Chapter 11） Timer/counter：T0, T1（Chapter 9） External memory accesses in 8031-based system：/WR, /RD（Chapter 14） ACOE343 - Embedded Real-Time Processor Systems - Frederick University

Port 3 Alternate Functions
17 RD P3.7 16 WR P3.6 15 T1 P3.5 14 T0 P3.4 13 INT1 P3.3 12 INT0 P3.2 11 TxD P3.1 10 RxD P3.0 Pin Function P3 Bit  ACOE343 - Embedded Real-Time Processor Systems - Frederick University

Generating Delays You can generate short delays using a register and incrementing or decrementing its value Example: mov r1, #0ah loop: djnz r1, loop How much delay is that? Djnz is a 2-byte instruction it takes two machine cycles One machine cycle is 1/12 of the system clock period For a 12 MHz system clock that is: Machine cycle = 12/12 = 1 MHz Machine period = 1/(1 MHz) = 10^(-6) s = 1 μs Loop time = 10*2*1 μs = 20 μs ACOE343 - Embedded Real-Time Processor Systems - Frederick University

Generating longer delays
Each register is 8 bits long, so it can increment 256 times before overflowing For larger delays, or when interrupts are required 8051 uses two timers ACOE343 - Embedded Real-Time Processor Systems - Frederick University

TMOD Register: Gate : When set, timer only runs while INT(0,1) is high. C/T : Counter/Timer select bit. M1 : Mode bit 1. M0 : Mode bit 0. ACOE343 - Embedded Real-Time Processor Systems - Frederick University

TCON Register: TF1: Timer 1 overflow flag. TR1: Timer 1 run control bit. TF0: Timer 0 overflag. TR0: Timer 0 run control bit. IE1: External interrupt 1 edge flag. IT1: External interrupt 1 type flag. IE0: External interrupt 0 edge flag. IT0: External interrupt 0 type flag. ACOE343 - Embedded Real-Time Processor Systems - Frederick University

Timer Mode Register Bit 7: Gate bit; when set, timer only runs while \INT high. (T0) Bit 6: Counter/timer select bit; when set timer is an event counter when cleared timer is an interval timer (T0) Bit 5: Mode bit 1 (T0) Bit 4: Mode bit 0 (T0) Bit 3: Gate bit; when set, timer only runs while \INT high. (T1) Bit 2: Counter/timer select bit; when set timer is an event counter when cleared timer is an interval timer (T1) Bit 1: Mode bit 1 (T1) Bit 0: Mode bit 0 (T1) ACOE343 - Embedded Real-Time Processor Systems - Frederick University

Timer Modes M1-M0: 00 (Mode 0) – 13-bit mode (not commonly used) M1-M0: 01 (Mode 1) - 16-bit timer mode M1-M0: 10 (Mode 2) - 8-bit auto-reload mode M1-M0: 11 (Mode 3) – Split timer mode ACOE343 - Embedded Real-Time Processor Systems - Frederick University

Timer Control Register (TCON)
Bit 7 (TF1) 8FH : Timer 1 overflow flag; set by hardware upon overflow, cleared by software Bit 6 (TR1) 8EH: Timer 1 run-control bit; manipulated by software - setting starts timer 1, resetting stops timer 1 Bit 5 (TF0) 8DH: Timer 0 overflow flag; set by hardware upon overflow, cleared by software. Bit 4 (TR0) 8CH: Timer 0 run-control bit; manipulated by software - setting starts timer 0, resetting stops timer 0 Bit 3 (IE1) 8BH: External 1 Interrupt flag bit Bit 2 (IT1) 8AH: Bit 1 (IE0) 89H: External 0 Interrupt flag bit Bit 0 (IT0) 88H: ACOE343 - Embedded Real-Time Processor Systems - Frederick University

Initializing and stopping timers
MOV TMOD, #16H ;initialization SETB TR0 ;starting timers SETB TR1 CLR TR0 ; stop timer 0 CLR TR1 ; stop timer 1 MOV R7, TH0 ; reading timers MOV R6, TL0 ACOE343 - Embedded Real-Time Processor Systems - Frederick University

Reading timers on the fly
Reading the Timers on the Fly To read the contents of a timer while it is running (ie; on the fly) poses a problem. MOV A, TH0 ;Let TH0 = 07 and TL0 = FF MOV R6, TL0 ;Now TH0=08 and TL0=00 but A=07 and R6=00! The solution is to read the high byte, then read the low byte, then read the high byte again. If the two readings of the low-byte are not the same repeat the procedure. The code for this method is detailed below. tryAgain:MOV A, TH0 MOV R6, TL0 CJNE A, TH0, tryAgain if the first reading of the hi-byte (in A) is not equal to current reading in the hi-byte (TH0) try againMOV R7, A; if both readings of the hi-byte are the same move the first reading into R7 - the overall reading is now in R7R6 ACOE343 - Embedded Real-Time Processor Systems - Frederick University

Generating delays using the timers
To generate a 50 ms (or 50,000 us) delay we start the timer counting from 15,536. Then, 50,000 steps later it will overflow. Since each step is 1 us (the timer's clock is 1/12 the system frequency) the delay is 50,000 us. 0 MOV TMOD, #10H; set up timer 1 as 16-bit interval timer CLR TR1 ; stop timer 1 (in case it was started in some other subroutine) MOV TH1, #3CH MOV TL1, #0B0H ; load 15,536 (3CB0H) into timer 1 SETB TR1 ; start timer 1 JNB TF1, $; repeat this line while timer 1 overflow flag is not set CLR TF1; timer 1 overflow flag is set by hardware on transition from FFFFH - the flag must be reset by software CLR TR1 ; stop timer 1 ACOE343 - Embedded Real-Time Processor Systems - Frederick University

Generating long delays
If the microcontroller has a system clock frequency of 12 MHz then the longest delay we can get from either of the timers is 65,536 usec. To generate delays longer than this, we need to write a subroutine to generate a delay of (for example) 50 ms and then call that subroutine a specific number of times. ... MOV TMOD, #10H; set up timer 1 as 16-bit interval timer fiftyMsDelay:CLR TR1 ; stop timer 1 (in case it was started in some other subroutine) MOV TH1, #3CH MOV TL1, #0B0H ; load 15,536 (3CB0H) into timer 1 SETB TR1 ; start timer 1 JNB TF1, $; repeat this line while timer 1 overflow flag is not set CLR TF1; timer 1 overflow flag is set by hardware on transition from FFFFH - the flag must be reset by software CLR TR1 ; stop timer 1 RET oneSecDelay:PUSH PSW PUSH AR0 ; save processor status MOV R0, #20 ; move 20 (in decimal) into R0 loop:CALL fiftyMsDelay ; call the 50 ms delay DJNZ R0, loop ; 20 times - resulting in a 1 second delay POP AR0 POP PSW ; retrieve processor status RET ACOE343 - Embedded Real-Time Processor Systems - Frederick University

Using timers to measure execution time
Timers are often used to measure the execution time of a program ORG 0H MOV TMOD, #16H ;initialization SETB TR0 ;starting timer 0 … ;main … ;program CLR TR0 ; stop timer 0 MOV R7, TH0 ; reading timer 0 MOV R6, TL0 ACOE343 - Embedded Real-Time Processor Systems - Frederick University

Interrupt : ACOE343 - Embedded Real-Time Processor Systems - Frederick University

Interrupt Enable Register :
EA : Global enable/disable. : Undefined. ET2 :Enable Timer 2 interrupt. ES :Enable Serial port interrupt. ET1 :Enable Timer 1 interrupt. EX1 :Enable External 1 interrupt. ET0 : Enable Timer 0 interrupt. EX0 : Enable External 0 interrupt. ACOE343 - Embedded Real-Time Processor Systems - Frederick University

Interrupt handling 8051 Interrupt Vector Table ACOE343 - Embedded Real-Time Processor Systems - Frederick University

Interrupt Service Routines
ORG 0 JMP main ORG 0003H ; external interrupt 0 vector …. ; interrupt handler code for external interrupt 0 RETI ORG 0013H ; external interrupt 1 vector …. ;interrupt handler code for external interrupt 1 RETI ORG 0030H ; main program main:SETB IT0 ; set external interrupt 0 as edge activated SETB IT1 ; set external interrupt 1 as edge activated SETB EX0 ; enable external interrupt 0 SETB EX1 ; enable external interrupt 1 SETB EA ; global interrupt enable … ACOE343 - Embedded Real-Time Processor Systems - Frederick University

Examples Write a 8051 assembly program that matches 8 switches with 8 LEDs Write a 8051 assembly program that uses a two-digit SSD to display the temperature as input from an ADC. Assume that the 0-5V range corresponds to 0-50 °C. The ADC uses RD, WR and INT pins. ACOE343 - Embedded Real-Time Processor Systems - Frederick University

8051 Programming Using C

Programming microcontrollers using high-level languages
Most programs can be written exclusively using high-level code like ANSI C Extensions To achieve low-level (Assembly) efficiency, extensions to high-level languages are required Restrictions Depending on the compiler, some restrictions to the high-level language may apply ACOE343 - Embedded Real-Time Processor Systems - Frederick University

Keil C keywords data/idata: Description: The variable will be stored in internal data memory of controller. example: unsigned char data x; //or unsigned char idata y; bdata: Description: The variable will be stored in bit addressable memory of controller. example: unsigned char bdata x; //each bit of the variable x can be accessed as follows x ^ 1 = 1; //1st bit of variable x is set x ^ 0 = 0; //0th bit of variable x is cleared xdata: Description: The variable will be stored in external RAM memory of controller. example: unsigned char xdata x; ACOE343 - Embedded Real-Time Processor Systems - Frederick University

Keil C keywords code: Description: This keyword is used to store a constant variable in code and not data memory. example: unsigned char code str="this is a constant string"; _at_: Description: This keyword is used to store a variable on a defined location in ram. example: CODE: unsigned char idata x _at_ 0x30; // variable x will be stored at location 0x30 // in internal data memory sbit: Description: This keyword is used to define a special bit from SFR (special function register) memory. example: sbit Port0_0 = 0x80; // Special bit with name Port0_0 is defined at address 0x80 ACOE343 - Embedded Real-Time Processor Systems - Frederick University

Keil C keywords sfr: Description: sfr is used to define an 8-bit special function register from sfr memory. example: sfr Port1 = 0x90; // Special function register with name Port1 defined at addrress 0x90 sfr16: Description: This keyword is used to define a two sequential 8-bit registers in SFR memory. example: sfr16 DPTR = 0x82; // 16-bit special function register starting at 0x82 // DPL at 0x82, DPH at 0x83 using: Description: This keyword is used to define register bank for a function. User can specify register bank 0 to 3. example: void function () using 2{ // code } // Funtion named "function" uses register bank 2 while executing its code Interrupt: Description: defines interrupt service routine void External_Int0() interrupt 0{ //code } ACOE343 - Embedded Real-Time Processor Systems - Frederick University

Pointers //Generic Pointer char * idata ptr; //character pointer stored in data memory int * xdata ptr1; //Integer pointer stored in external data memory //Memory Specific pointer char idata * xdata ptr2; //Pointer to character stored in Internal Data memory //and pointer is going to be stored in External data memory int xdata * data ptr3; //Pointer to character stored in External Data memory //and pointer is going to be stored in data memory ACOE343 - Embedded Real-Time Processor Systems - Frederick University

Writing hardware-specific code
#include <REGx51.h> //header file for 89C51 void main(){ //main function starts unsigned int i; //Initializing Port1 pin1 P1_1 = 0; //Make Pin1 o/p while(1){ //Infinite loop main application //comes here for(i=0;i<1000;i++) ; //delay loop P1_1 = ~P1_1; //complement Port1.1 //this will blink LED connected on Port1.1 } } ACOE343 - Embedded Real-Time Processor Systems - Frederick University

C and Assembly together
extern unsigned long add(unsigned long, unsigned long); void main(){ unsigned long a; a = add(10,30); //calling Assembly function while(1); } ACOE343 - Embedded Real-Time Processor Systems - Frederick University

C and Assembly together
name asm_test ?PR?_add?asm_test segment code ?DT?_add?asm_test segment data ;let other function use this data space for passing variables public ?_add?BYTE ;make function public or accessible to everyone public _add ;define the data segment for function add rseg ?DT?_add?asm_test ?_add?BYTE: parm1: DS 4 ;First Parameter parm2: ds 4 ;Second Parameter ;either you can use parm1 for reading passed value as shown below ;or directly use registers used to pass the value. rseg ?PR?_add?asm_test _add: ;reading first argument mov parm1+3,r7 mov parm1+2,r6 mov parm1+1,r5 mov parm1,r4 ;param2 is stored in fixed location given by param2 ;now adding two variables mov a,parm2+3 add a,parm1+3 ;after addition of LSB, move it to r7(LSB return register for Long) mov r7,a mov a,parm2+2 addc a,parm1+2 ;store second LSB mov r6,a mov a,parm2+1 addc a,parm1+1 ;store second MSB mov r5,a mov a,parm2 addc a,parm1 mov r4,a ret end ACOE343 - Embedded Real-Time Processor Systems - Frederick University

The infinite loop A loop with no termination condition or one that will never be met may be unwanted in computer systems, but common in embedded systems. ACOE343 - Embedded Real-Time Processor Systems - Frederick University

Example 1 Generate a 5V peek-to-peek 200μs period square waveform on the DAC output ACOE343 - Embedded Real-Time Processor Systems - Frederick University

Example 2 Generate a 5V peek-to-peek 200μs period sawtooth waveform on the DAC output ACOE343 - Embedded Real-Time Processor Systems - Frederick University

Example 3 Generate a 5V peek-to-peek 2ms period sine waveform on the DAC output code unsigned char Sine[180] = { /* Sine values */ 127,131,136,140,145,149,153,158,162,166,170,175, 179,183,187,191,194,198,202,205,209,212,215,218, 221,224,227,230,232,235,237,239,241,243,245,246, 248,249,250,251,252,253,253,254,254,254,254,254, 253,253,252,251,250,249,248,246,245,243,241,239, 237,235,232,230,227,224,221,218,215,212,209,205, 202,198,194,191,187,183,179,175,170,166,162,158, 153,149,145,140,136,131,127,123,118,114,109,105, 101, 96, 92, 88, 84, 79, 75, 71, 67, 64, 60, 56, 52, 49, 45, 42, 39, 36, 33, 30, 27, 24, 22, 19, 17, 15, 13, 11, 9, 8, 6, 5, 4, 3, 2, 1, 1, 0, 0, 0, 0, 0, 1, 1, 2, 3, 4, 5, 6, 8, 9, 11, 13, 15, 17, 19, 22, 24, 27, 30, 33, 36, 39, 42, 45, 49, 52, 56, 60, 63, 67, 71, 75, 79, 84, 88, 92, 96, 101,105,109,114,118 }; /************************************************************ * START of the PROGRAM * ************************************************************ / void main (void) { unsigned char i; * Enable the D/A Converter * ENDAC0 = 1; /* Enable DAC0 */ * Create the waveforms on DAC0 * while(1){ /* Run for ever */ for(i = 0; i < 179; i++) DAC0 = Sine[i]; } * while(1) */ } /* main() */ } ACOE343 - Embedded Real-Time Processor Systems - Frederick University

Mixed C/Assembly code (μVision Version 2.06)
Parameter passing in registers Examples: ACOE343 - Embedded Real-Time Processor Systems - Frederick University

Function return values
ACOE343 - Embedded Real-Time Processor Systems - Frederick University

Example extern unsigned char add2_func(unsigned char, unsigned char); void main(){ unsigned char a; a = add2_func(10,30); //a will have 40 after execution while(1); } ;assembly file “add2.asm” NAME _Add2_func ?PR?add2_func?Add2 SEGMENT CODE PUBLIC add2_func RSEG ?PR?Add2_func?Add2 add2_func: mov a, r7 ;first parameter passed to r7 add a, r5 ;second parameter passed to r5 mov r7, a ;return parameter must be in r7 RET END ACOE343 - Embedded Real-Time Processor Systems - Frederick University

Calling C from Assembly
NAME A_FUNC ?PR?a_func?A_FUNC SEGMENT CODE EXTRN CODE (c_func) PUBLIC a_func RSEG ?PR?a_func?A_FUNC a_func: USING 0 LCALL c_func RET END void c_func (void) { } ACOE343 - Embedded Real-Time Processor Systems - Frederick University

Data Converters Analog to Digital Converters (ADC)
Convert an analog quantity (voltage, current) into a digital code Digital to Analog Converters (DAC) Convert a digital code into an analog quantity (voltage, current) Dr. Konstantinos Tatas and Dr. Costas Kyriacou

Video (Analog - Digital)
Modulator Amplifier Filters Analog Pre- amplifier A/D Digital Image enhancement and coding ACOE343 - Embedded Real-Time Processor Systems - Frederick University

Temperature Recording by a Digital System
Time Temperature (ºC) Time Sampling & quantization Coding ACOE343 - Embedded Real-Time Processor Systems - Frederick University

Need for Data Converters
Digital processing and storage of physical quantities (sound, temperature, pressure etc) exploits the advantages of digital electronics Better and cheaper technology compared to the analog More reliable in terms of storage, transfer and processing Not affected by noise Processing using programs (software) Easy to change or upgrade the system (e.g. Media Player 7  Media Player 8 ή Real Player) Integration of different functions (π.χ. Mobile = phone + watch + camera + games + + ACOE343 - Embedded Real-Time Processor Systems - Frederick University

Signals (Analog - Digital)
2 4 6 8 10 12 14 16 u(V) 1 7 3 5 9 t (S) Analog Signal can take infinity values can change at any time 1010 1110 1111 1100 1000 Digital Signal can take one of 2 values (0 or 1) can change only at distinct times Reconstruction of an analog signal from a digital one (Can take only predefined values) 1001 0110 0101 0100 2 4 6 8 10 12 14 16 u(V) 1 7 3 5 9 t (S) ADC 1001 0110 0101 1010 1111 1110 1000 1100 0100 D3 D2 D1 D0 1 1 1 1 1 DAC ACOE343 - Embedded Real-Time Processor Systems - Frederick University

QUANTIZATION ERROR The difference between the true and quantized value of the analog signal Inevitable occurrence due to the finite resolution of the ADC The magnitude of the quantization error at each sampling instant is between zero and half of one LSB. Quantization error is modeled as noise (quantization noise) ACOE343 - Embedded Real-Time Processor Systems - Frederick University

SAMPLING FREQUENCY (RATE)
The frequency at which digital values are sampled from the analog input of an ADC A low sampling rate (undersampling) may be insufficient to represent the analog signal in digital form A high sampling rate (oversampling) requires high bitrate and therefore storage space and processing time A signal can be reproduced from digital samples if the sampling rate is higher than twice the highest frequency component of the signal (Nyquist-Shannon theorem) Examples of sampling rates Telephone: 4 KHz (only adequate for speech, ess sounds like eff) Audio CD: 44.1 KHz Recording studio: 88.2 KHz ACOE343 - Embedded Real-Time Processor Systems - Frederick University

Digital to Analog Converters
Vout (mV) 1 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 The analog signal at the output of a D/A converter is linearly proportional to the binary code at the input of the converter. If the binary code at the input is 0001 and the output voltage is 5mV, then If the binary code at the input becomes 1001, the output voltage will become 45mV If a D/A converter has 4 digital inputs then the analog signal at the output can have one out of …… values. 16 If a D/A converter has N digital inputs then the analog signal at the output can have one out of ……. values. 2Ν ACOE343 - Embedded Real-Time Processor Systems - Frederick University

Characteristics of Data Converters
Number of digital lines The number bits at the input of a D/A (or output of an A/D) converter. Typical values: 8-bit, 10-bit, 12-bit and 16-bit Can be parallel or serial Microprocessor Compatibility Microprocessor compatible converters can be connected directly on the microprocessor bus as standard I/O devices They must have signals like CS, RD, and WR Activating the WR signal on an A/D converter starts the conversion process. Polarity Polar: the analog signals can have only positive values Bipolar: the analog signals can have either a positive or a negative value Full-scale output The maximum analog signal (voltage or current) Corresponds to a binary code with all bits set to 1 (for polar converters) Set externally by adjusting a variable resistor that sets the Reference Voltage (or current) ACOE343 - Embedded Real-Time Processor Systems - Frederick University

Characteristics of Data Converters (Cont…)
Resolution The analog voltage (or current) that corresponds to a change of 1LSB in the binary code It is affected by the number of bits of the converter and the Full Scale voltage (VFS) For example if the full-scale voltage of an 8-bit D/A converter is 2.55V the the resolution is: VFS/(2N-1) = 2.55 /(28-1) 2.55/255 = 0.01 V/LSB = 10mV/LSB Conversion Time The time from the moment that a “Start of Conversion” signal is applied to an A/D converter until the corresponding digital value appears on the data lines of the converter. For some types of A/D converters this time is predefined, while for others this time can vary according to the value of the analog signal. Settling Time The time needed by the analog signal at the output of a D/A converter to be within 10% of the nominal value. ACOE343 - Embedded Real-Time Processor Systems - Frederick University

ADC RESPONSE TYPES Linear Most common Non-linear Used in telecommunications, since human voice carries more energy in the low frequencies than the high. ACOE343 - Embedded Real-Time Processor Systems - Frederick University

ADC TYPES Direct Conversion Fast Low resolution Successive approximation Low-cost Slow Not constant conversion delay Sigma-delta High resolution, low-cost, high accuracy ACOE343 - Embedded Real-Time Processor Systems - Frederick University

Interfacing with Data Converters
Microprocessor compatible data converters are attached on the microprocessor’s bus as standard I/O devices. ACOE343 - Embedded Real-Time Processor Systems - Frederick University

Programming Example 1 Write a program to generate a positive ramp at the output of an 8-bit D/A converter with a 2V amplitude and a 1KHz frequency. Assume that the full scale voltage of the D/A converter is 2.55V. The D/A converter is in P0 and the WR signal is in P1.1 main() { do { for (i=0;i<200;i++) P1_0=1; P0=i; delayu(5); } } while (1) ACOE343 - Embedded Real-Time Processor Systems - Frederick University

D/A Converters example
Write a program to generate the waveform, shown below, at the output of an 8-bit digital to analog converter. The period of the waveform should be approximately 8 ms. Assume that a time delay function with a 1 μs resolution is available. The full scale output of the converter is 5.12 V and the address of the DAC is P0, while the WR signal is in P1.1. Assuming that an 8-bit A/D converter is used to interface a temperature sensor measuring temperature values in the temperature range , specify: The resolution in of the system in The digital output word for a temperature of 32.5 The temperature corresponding to a digital output word of ACOE343 - Embedded Real-Time Processor Systems - Frederick University

Programming the 8051 Microcontroller Dr. Konstantinos Tatas

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