6502   MICROPROCESSOR SUMMARY

There is little difference between the 6502 and the 6512 (as used in the Commodore range of home computers such as the C64.); the main being the 6512's need for an external two phase clock and the incorporation of a DBE (data bus enable) for external Data Bus tri-state control.

Features:

On-chip timing generator requires ext. single phase oscillator 1MHz (6502) or 2MHz (6502A)

64K addressable memory

Two phase clock output for 6800 series supporting chips

Single general purpose 8 bit Accumulator

Two 8 bit Index registers

Zero page addressing allows for faster processing and shorter program code

Single +5V supply

1

Ground

2

A negative transition halts the MPU. Allows for single step cycling etc.

3

CK 1 OUT      Phase 1 clock output

4

/IRQ      If interrupt mask flag is not set, program counter jumps to FFFE & FFFF

5

n/c-

6

/NMI      Non-maskable interrupt requires low condition to jump to FFFA & FFFB

7

Sync      Identifies the op-code fetch instructions

8

Vcc      +5V

9-20

A0-11

22-25

A12-15      Address bus

21

Vss      Ground

26-33

D0-7      Bi-directional / tristate data bus

34

R /W      Read / Write line

35

n/c      -

36

n/c      -

37

CK in      Single phase clock input

38

/SO      Neg. input sets the overflow flag. Must be in sync. with CK1 trailing edge

39

CK 2 OUT      Phase 2 clock output

40

/RES      A low initialises the MPU and sets the program counter to FFFC & FFFD