The Western Design Center, Inc.

W65C02S Datasheet

The Western Design Center, Inc.

W65C02S Datasheet

36

7 CAVEATS

Table 7-1 Microprocessor Operational Enhancements

Function

NMOS 6502

W65C02S

Indexed addressing across page

boundary

Extra read of invalid address.

Extra read of last instruction byte.

Execution of invalid OpCodes.

Some terminate only by reset.

Results are undefined.

All are NOP's (reserved for future use).

OpCode

Bytes

Cycles

02,22,42,62,82

2

2

C2, E2

X3,OB-BB,EB,FB

1

1

44

2

3

54,D4,F4

2

4

5C

3

8

DC,FC

3

4

Jump indirect, operand = XXFF.

Page address does not increment.

Page address increments, one additional

cycle.

Read/Modify/Write instruction at

effective address.

One read and two write cycles.

Two read and one write cycle.

Decimal flag.

Indeterminate after reset.

Initialized to binary mode (D=0) after reset

and interrupts.

Flags after decimal operation.

Invalid N, V and Z flags.

Valid flags. One additional cycle.

Interrupt after fetch of BRK

instruction

Interrupt vector is loaded; BRK

vector is ignored.

BRK is executed, and then interrupt is

executed.

Ready.

Input.

Bi-directional, WAI instruction pulls low.

Read/Modify/Write instructions

absolute indexed in same page.

Seven cycles.

Six cycles.

Oscillator.

Requires external active components.

Crystal or RC network will oscillate when

connected between PHI2 and PHI10.

Assertion of Ready (RDY) during

write operations.

Ignored.

Stops p rocessor during PHI2, and WAI

instruction pulls RDY low.

Clock inputs.

PHI2 is the only required clock.

PHI2 is the only required clock.

Unused input-only pins.

Must be tied to VDD.

Must be tied to VDD.

The BRK instruction for both the NMOS 6502 and 65C02 is a 2 byte instruction. The NMOS and CMOS devices

simply skips the second byte (i.e. doesn’t care about the second byte) by incrementing the program counter twice.

It is important to realize that if a return from interrupt is used it will return to the location after the second or

signature byte.