AN910 datasheet(28/51 Pages) STMICROELECTRONICS

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ST7 AND ST9 PERFORMANCE BENCHMARKING

7.3.1 80C51XA MCU core

On-chip/Off-chip buses

- on-chip buses

16-bit address bus (up to 24-bit)

8/16-bit data memory bus

8/16-bit program memory bus

8/16-bit sfr bus

- off-chip buses

8/16-bit address bus (up to 24-bit)

8/16-bit multiplexed sfr/data/program mem. bus

the two buses may be multiplexed

the two buses are multiplexed with ports

Memory Spaces

Harvard organization

- segmented data/program memory spaces

data memory space

up to 255 segments of 64 kbytes each = 16 Mbytes

1-Kbyte zero page/segment (32 bytes bit addr.)

special function register space (logically separate)

512 bytes of on-chip registers (64 bytes bit addr.)

512 bytes of off-chip registers

program memory space

up to 255 segments of 64 kbytes each = 16 Mbytes

first 284-byte interrupt vector table = 71 interrupts

Arithmetic Logic Unit

16-bit datapath

- 8/16-bit operations

- special functions

8x8 unsigned multiplication

12 cycles

16x16 (un)signed multiplications

12 cycles

8/8 unsigned division

12 cycles

16/8 (un)signed divisions

(12)14 cycles

32/16 (un)signed divisions

(22)24 cycles

32-bit shifts

6 cycles

Instruction processing

Prefetch mechanism

- 7-byte queue

- predecoding

- jump/branch address even alignment

addition of some 1-byte NOP instructions

- word operand even alignment

addition of some 1-byte NOP instructions

Cpu internal buses

16-bit mux. address/data/control bus

8/16-bit sfr bus (special function register)

Instruction set

Cisc encoding

- CPI

2 cycles to 24 cycles

- average CPI

between 5 and 6 cycles

- IL

2 bytes to 6 bytes

- average IL

between 3 and 4 bytes

- special addressing modes

immediate with 11-bit addresses

indirect with 8/16-bit offset or auto-increment

- special instructions

exchange register contents

push/pull multiple registers

memory-to-memory moves

compare & branch like

decrement & branch like

Programming model

- banked registers

4 banks of four 16-bit registers

- global registers

four 16-bit registers (up to 12)

- others registers

16-bit program counter (up to 24-bit)

two 8-bit segment registers

16-bit system and user stack pointers

- special function registers

program status word, system configuration register

segment select register

data/extra/code segment registers

on-chip/off-chip peripheral and i/o port registers

- multitasking capabilities

context switching with banked registers

system and user modes

MOVE Rd,Rs

ADD

Rd,#2

+ / x

80C51XA CPU

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