8051 hardware summary

Transcription

1 8051 hardware summary

2 8051 block diagram

3 8051 pinouts + 5V

4 ports port 0 port 1 port 2 port 3 : dual-purpose (general-purpose, external memory address and data) : dedicated (interfacing to external devices) : dual-purpose (general-purpose, external memory address and data) : dual-purpose (general-purpose, special features)

5 port 3 special features

6 bus control signals PSEN ALE EA RST : Program Store Enable (enables external program memory) : Address Latch Enable (demultiplexing the address and data bus) : External Access (program execution from external or internal memory, programming of internal PEROM) : Reset (system start-up)

7 on-chip oscillator inputs on-chip oscillator can either be driven by a crystal (~ 12 MHz) or a TTL clock source

8 I/O port structure 4 low-power Schottky TTL loads for ports 1, 2, 3 8 LS loads for Port 0

9 pull-up / pull-down resistors

10 TTL vs. CMOS Transistor-Transistor Logic BJTs (Bipolar Junction Transistor) + resistors low power consumption (more power consumption at rest, however it does not increase much with clock speed compared to CMOS) easier design rules slower Complementarysymmetry Metal-Oxide- Semiconductor MOSFETs (Metal-Oxide- Semiconductor Field- Effect-Transistors) high power consumption (it increases dramatically with clock speed) harder to design faster

11 TTL vs. CMOS (cont d) TTL NAND gate CMOS NAND gate

12 memory organization 128B internal RAM 4KB ROM can be expanded to 64KB code memory and 64KB data memory registers and I/O ports are memory-mapped and accessible like any other memory location stack resides within the internal RAM (unlike microprocessors using external RAM for stack)

13 internal RAM

14 general-purpose RAM 80B MOV direct addressing A, 5FH MOV R0, #5FH MOV indirect addressing 00H 2FH can be used as similar (80B + 48B = 128B) any location in the general-purpose RAM can be accessed freely using direct and indirect addressing modes

15 bit-addressable RAM 210 bit-addressable locations individually accessing bits SETB 67H microcontroller MOV A, 2CH ORL A, # B MOV 2CH, A microprocessor

16 register banks PSW context-switching default by system reset MOV A, R5 register addressing 1B MOV A, 05H direct addressing 2B

17 Special Function Registers 21 SFRs some of them are both bitaddressable and byteaddressable SETB E0H E0H : bit-address of the accumulator E0H : byte-address of the accumulator P0 : 80H (80H 87H) {10000xxx}

18 Program Status Word

19 CarrY flag of PSW arithmetic operations boolean accumulator ADD A, #1 ; A = FFH ANL C, 25H CY is set result is stored in CY

20 Auxiliary Carry flag of PSW checks the lower nibble of result in BCD addition XXXX 1010 if {0AH OFH} AC is set DA A ; Decimal Adjust Accumulator (result back in range 9) DA must follow the addition

21 Flag 0 of PSW general-purpose flag bit, F0 (for user applications)

22 Register bank Select bits of PSW SETB SETB MOV RS1 RS0 A, R7

23 OVerflow flag of PSW when unsigned numbers are added or subtracted, OV can be ignored when signed numbers are added or subtracted, results out of {-128 to +127} sets OV

24 Parity bit of PSW P bit is automatically set or cleared with each machine cycle (even parity check on accumulator) if [number of 1 s in accumulator] + 1 = even then (P = 1)

25 B register MUL AB ; A(8-bit) X B(8-bit) = 16-bit result (high-byte, low-byte) DIV AB ; A(8-bit) / B(8-bit) = 8-bit integer result, 8-bit remainder it can also be used as a generalpurpose scratch-pad register

26 Stack Pointer 32B SS push -> first SP+1, then write data pop -> first read data, then SP-1 default by system reset : 07H MOV SP, #5FH ; beginning address of stack = 60H!!! be very careful of what you are doing if you do not initialize your own stack space but still use context switching, and PUSH, POP, ACALL, LCALL, RET, RETI instructions on stack space (SS)

27 Data PoinTeR high-byte - DPH low-byte - DPL accessing external code or external data memory MOV A, #55H ; immediate addressing MOV DPTR, #1000H ; immediate addressing A ; indirect addressing 55H

28 Port registers ports 0,2 and 3 may not be available for I/O if external memory is used or if some 8051 special features (interrupts, serial ports, etc.) are used P1.2 to P1.7 are always available for general purpose I/O lines WAIT: SETB P1.7 CLR P1.7 JB P1.5, WAIT 1 device busy 0 device ready

29 Timer registers two 16-bit timer/counters high-byte TH1 high-byte TH0 low-byte TL1 low-byte TL0 Timer MODe register Timer CONtrol register Timer 0 : {TH0, TL0} Timer 1 : {TH1, TL1} only TCON is bit-addressable

30 Serial port registers on-chip serial port for communicating with serial devices Serial data BUFfer (SBUF) holds both the transmit data (writing to buffer) and the receive data (reading from buffer) Various modes of operation on bitaddressable Serial port CONtrol register (SCON)

31 Interrupt registers 5-source, 2-priority level interrupt structure interrupts are disabled as default by system reset should be enabled by writing to the Interrupt Enable register (IE) priority level is set through the Interrupt Priority register (IP)

32 Power CONtrol register

33 IDLe mode an instruction that sets IDL bit will be the last instruction executed before entering idle mode CPU status preserved, all register contents are maintained port pins retain their logic levels ALE and PSEN are held high idle mode is terminated by any enabled interrupt or by system reset, either condition clears the IDL bit

34 Power Down mode an instruction that sets PD bit will be the last instruction executed before entering power down mode on-chip oscillator stopped all function are stopped all on-chip RAM contents are retained port pins retain their logic levels ALE and PSEN are held low only exit is system reset V CC can be as low as 2V in power down mode

35 external memory 64K external code memory space and 64K external data memory space can be made available by 8051 architecture when external memory is used P0 is unavaliable as an I/O port P0 becomes a multiplexed address (A0-A7) and data (D0-D7) bus with ALE latching the low-byte of the address at the beginning of each memory cycle if MOVX instructions are never used ALE pulses consistently at 1/6 of crystal frequency if MOVX instruction is used both ALE and PSEN pulses are skipped once on the RD line to enable the RAM

36 multiplexing address and data buses

37 accessing external code memory

38 read timing for external code memory

39 accessing external data memory

40 accessing external data memory (cont d) MOVX instruction MOVX SETB P2.0 SETB P2.1 MOV R0, #FFH MOVX read 03FFH

41 address decoding

42 external memory (cont d) increment RAM location by 1: it takes 1 instruction and 1 instruction cycles for internal RAM it takes 4 instructions and 7 instruction cycles for external RAM external memory is ~ 7 times slower size: internal RAM is limited to 128B external RAM up to 64KB

43 overlapping the external code and data spaces

44 von Neumann architecture stored program concept program can modify themselves on the run program faults can effect other programs, operating system leading to crash es memory protection and access control mechanisms against malware von Neumann bottleneck caches, branch prediction algorithms

45 Hardvard architecture separate storage and signal pathways for instructions and data modifying programs is entirely an offline process instruction memory often wider than data memory speed is gained at the expense of more complex electrical circuitry caches (high cost) for memory bound problem specialized DSPs (audio/video, etc.), small microcontrollers (PIC, etc.) modern high-performance CPU designs incorporate aspects of both von Neumann and Harvard architectures

46 ReSeT operation 8051 is reset by holding RST high for two machine cycles and then returning it low power-on reset manual reset

47 Register values after system ReSeT

48 summary 8051 architecture and layout memory organization Special Function Registers external memory

49 references