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8051- Microcontrollers Architecture & Addressing modes
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- 3. ⚫An example forCISC Processor . ⚫Harvard Architecture ⚫Collection of 8 and 16 bit registers and 8 bit memory locations. ⚫External Memory can be interfaced.
- 4. Pin Description ofthe 8051 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 40 39 38 37 36 35 34 33 32 31 30 29 28 27 26 25 24 23 22 21 P1.0 P1.1 P1.2 P1.3 P1.4 P1.5 P1.6 P1.7 RST (RX D)P 3.0 (TXD)P3.1 (I NT0)P3.2 (INT1)P3.3 (T0)P3.4 (T1)P3.5 (WR)P3.6 (RD)P3.7 XTAL2 XTAL1 GND Vcc P0.0(AD0) P0.1(AD1) P0.2(AD2) P0.3(AD3) P0.4(AD4) P0.5(AD5) P0.6(AD6) P0.7(AD7) EA/VPP ALE/PROG PSEN P2.7(A15) P2.6(A14) P2.5(A13) P2.4(A12) P2.3(A11) P2.2(A10) P2.1(A9) P2.0(A8) 8051
- 5. Pins of 8051 （1/4 ） ⚫ Vcc （ pin 40 ）： ⚫ Vcc provides supply voltage to the chip. ⚫ The voltage source is +5V. ⚫ GND （ pin 20 ）： ground ⚫ XTAL1 and XTAL2 （ pins 19,18 ）： ⚫ These 2 pins provide external clock.
- 6. P⚫inRsSoTf （ 8p0i5n 19（） 2 ： /4r ） eset ⚫ It is an input pin and is active high （ normally low ） . ⚫ Upon applying a high pulse to RST, the microcontroller will reset and all values in registers will be lost.
- 7. Pins of 8051（ 3/4 ） ⚫ /EA （ pin 31 ）： external access ⚫ The /EA pin is connected to GND to indicate the code is stored externally. ⚫ For 8051, /EA pin is connected to Vcc. ⚫ “/” means active low. ⚫ /PSEN （ pin 29 ）： program store enable ⚫ This is an output pin and is connected to the OE pin of the ROM
- 8. Pins of 8051（ 4/4 ） ⚫ ALE （ pin 30 ）： address latch enable ⚫ It is an output pin and is active high. ⚫ 8051 port 0 provides both address and data. ⚫ The ALE pin is used for de-multiplexing the address and data by connecting to the G pin of the 74LS373 latch. ⚫ I/O port pins ⚫ The four ports P0, P1, P2, and P3. ⚫ Each port uses 8 pins. ⚫ All I/O pins are bi-directional.
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- 10. ⚫Internal ROM andRAM ⚫I/O Ports with programmable Pins ⚫ALU ⚫Working Registers ⚫Clock Circuits ⚫Timers and Counters ⚫Serial Data Communication.
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- 12. Specific Features ⚫8 bitcpu with registers A and B ⚫16 bit PC and DPTR(data pointer). ⚫8 bit program status word(PSW) ⚫8 bit Stack Pointer ⚫4K Internal ROM ⚫128bytes Internal RAM - 4 register banks each having 8 registers 16 bytes,which may be addressed at the bit level. 80 bytes of general purpose data memory
- 13. Specific Features ⚫32 i/opins arranged as 4 8 bit ports:P0 to P3 ⚫Two 16 bit timer/counters:T0 and T1 ⚫Full duplex serial data receiver/transmitter ⚫Control registers:TCON,TMOD,SCON,PCON,IP and IE ⚫Two external and Three internal interrupt sources. ⚫Oscillator and Clock Circuits.
- 14. Pins of I/OPort ⚫ The 8051 has four I/O ports ⚫ Port 0 （ pins 32-39 ）： P0 （ P0.0 ～ P0.7 ） ⚫ Port 1 （ pins 1-8 ） ： P1 （ P1.0 ～ P1.7 ） ⚫ Port 2 （ pins 21-28 ）： P2 （ P2.0 ～ P2.7 ） ⚫ Port 3 （ pins 10-17 ）： P3 （ P3.0 ～ P3.7 ） ⚫ Each port has 8 pins. ⚫ Named P0.X （ X=0,1,...,7 ） , P1.X, P2.X, P3.X ⚫ Ex ： P0.0 is the bit 0 （ LSB ） of P0 ⚫ Ex ： P0.7 is the bit 7 （ MSB ） of P0 ⚫ These 8 bits form a byte. ⚫ Each port can be used as input or output (bi-direction).
- 15. Program Counter &Data Pointer ⚫They are both 16 bit registers. ⚫Each is to hold the address of a byte in memory ⚫PC contains the address of the next instruction to be executed. ⚫DPTR is made up of two 8 bit register DPH and DPL; ⚫DPTR contains the address of internal & external code and data that has to be accessed.
- 16. A and BCPU registers ⚫Totally 34 general purpose registers or working registers. ⚫Two of these A and B hold results of many instructions, particularly math and logical operations of 8051 cpu. ⚫The other 32 are in four banks,B0 – B3 of eight registers each. ⚫A(accumulator) is used for addition,subtraction,mul,div,boolean bit manipulation and for data transfers. ⚫But B register can only be used for mul and div operations.
- 17. 8051 Flag bitsand the PSW register ⚫PSW Register CY AC F0 RS1 RS0 OV -- P Carry flag PSW.7 CY Auxiliary carry flag PSW.6 AC Available to the user for general purpose PSW.5 -- Register Bank selector bit 1 PSW.4 RS1 Register Bank selector bit 0 PSW.3 RS0 Overflow flag PSW.2 OV User define bit PSW.1 -- Parity flag Set/Reset odd/even parity PSW.0 P RS1 RS0 Register Bank Address 0 0 0 00H-07H 0 1 1 08H-0FH 1 0 2 10H-17H 1 1 3 18H-1FH
- 18. • Two flagbits are stored in PCON(Power control) registers also. •They are the GF1 (3RD) and GF0(2nd) bits • They are general purpose user flag bit 1 and 0 respectively •They can be set or cleared by the program •For more details of PCON, refer fig 3.13 in text book.
- 19. ⚫RAM memory spaceallocation in the 8051 7FH 30H 2FH 20H 1FH 10H 0FH 08H 07H 18H 17H 00H Register Bank 0 (Stack) Register Bank 1 Register Bank 2 Register Bank 3 Bit-Addressable RAM Scratch pad RAM Memory Organization
- 20. Stack in the8051 ⚫ 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 10H 0FH 08H 07H 18H 17H 00H Register Bank 0 (Stack) Register Bank 1 Register Bank 2 Register Bank 3 Bit-Addressable RAM Scratch pad RAM
- 21. Special Function Registers NameFunction Name Function A Accumulator SBUF Serial Port data buffer B Arithmetic SP Stack Pointer DPH Addressing Ext Memory TMOD Timer/ Counter mode cntrl DPL Addressing Ext Memory TCON Timer/Counter cntrl IE Interrupt enable TL0 Timer0 lower byte IP Interrupt Priority TH0 Timer0 higher byte P0 I/O Port Latch TL1 Timer1 lower byte P1 I/O Port Latch TH1 Timer1 higher byte P2 I/O Port Latch P3 I/O Port Latch PCON Power Control PSW Pgm Status Word
- 22. Port 0 （pins 32-39 ） ⚫When connecting an 8051 to an external memory, the 8051 uses ports to send addresses and read instructions. ⚫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. I/O Port Programming
- 23. Port 1 （pins 1- 8 ） ⚫ Port 1 is denoted by P1. ⚫ P1.0 ~ P1.7 ⚫ 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)
- 24. ALE Pin ⚫The ALEpin 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.
- 25. P⚫oArltth3ou （ ghppoirnt 3sis1c0on- f1ig7ur ） ed 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 ⚫External interrupt ： /INT0, /INT1 ⚫Timer/counter ： T0, T1 ⚫External memory accesses ： /WR, /RD
- 26. Port 3 Alternate Functions P3Bit Function Pin P3.0 RxD 10 P3.1 TxD 11 P3.2 INT0 12 P3.3 INT1 13 P3.4 T0 14 P3.5 T1 15 P3.6 WR 16 P3.7 RD 17
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- 28. Immediate Addressing Mode ⚫ImmediateData is specified in the instruction itself ⚫Egs: MOV A,#65H MOV A,#’A’ MOV R6,#65H MOV DPTR,#2343H MOV P1,#65H
- 29. Register Addressing Mode MOVRn, A ;n=0,..,7 ADD A, Rn MOV DPL, R6 MOV DPTR, A MOV Rm, Rn
- 30. Direct Addressing Mode Althoughthe 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 6, 2 ; ≡ MOV A, R4 ; copy R2 to R6 ; MOV R6,R2 is invalid !
- 31. Register Indirect AddressingMode ⚫In this mode, register is used as a pointer to the data. MOV A,@Ri ; 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. jump
- 32. Indexed Addressing ModeAnd 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,@A+DPTR 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.