NT68P81

5

Functional Description

1. 6502C CPU

The 6502C is an 8 -bit CPU that provides 56 instructions, decimal and binary arithmetic, thirteen addressing modes, true

indexing capability, programmable stack pointer and variable length stack, a wide selection of addressable memory

range, and an interrupt input. Other features are also included.

The CPU clock cycle is 3MHz (6MHz system clock divided by 2). Please refer to 6502 data sheet for more detailed

information.

Accumulator A

Index Register Y

0

7

7

Index Register X

7

0

0

Stack Pointer SP

0

N

Status Register P

0

7

Carry

Zero

IRQ Disable

Decimal Mode

BRK Command

Overflow

Negative

7

Program Counter PCH

8

15

7

0

PCL

1 = TRUE

1 = Result ZERO

1 = DISABLE

1 = TRUE

1 = NEG

1 = TRUE

1 = BRK

V

B

D

I

Z

C

Figure 1. 6502 CPU Registers and Status Flags