|System Specification for C65||Fred Bowen||March 1, 1991|
The 4502, upon reset, looks and acts like any other CMOS 6502 Processor, with the exception that many instructions are shorter or require less cycles than they used to. This causes programs to execute in less time that older versions, even at the same clock frequency,
The stack pointer has been expanded to 16 bits, but can be used in two different modes. It can be used as a full 16-bit (word) stack pointer, or as an 8-bit (byte) pointer whose stack page is programmable. On reset, the byte mode is selected with page I set as the stack page. This is done to make it fully 65CO2 compatible.
The zero page is also programmable via a new register, the "B" or "Base Page" register. On reset, this register is cleared, thus giving a true "zero" page for compatability reasons, but the user can define any page in memory as the "zero" page.
A third index register, "Z", has been added to increase flexibility in data manipulation. This register is also cleared, on reset, so that the STZ instructions still do what they used to, for compatability.
This is a list of opcodes that have been added to the 210 previously defined MOS, Rockwell, and GTE opcodes.
1. Branches and Jumps
BCC label word-relative BCS label word-relative BEQ label word-relative BMI label word-relative BNE label word-relative BPL label word-relative BRA label word-relative BVC label word-relative BVS label word-relative BSR label Branch to subroutine (word relative) JSR (ABS) Jump to subroutine absolute indirect JSR (ABS,X) Jump to subroutine absolute indirect, X RTN # Return from subroutine and adjust stack pointer.
2. Arithmetic Operations
NEG A Negate (or 2's complement) accumulator. ASR A Arithmetic Shift right accumulator or memory ASR ZP ASR ZP,X INW ZP Increment Word DEW ZP Decrement Word INZ Increment and DEZ Decrement Z register ASW ABS Arithmetic Shift Left Word ROW ABS Rotate Left Word ORA (ZP),Z These were formerly (ZP) non-indexed AND (ZP),Z now are indexed by Z register EOR (ZP),Z (when Z=O, operation is the same)
|This page has been created by Sami Rautiainen.|
|Read the small print.||Last updated April 06, 2006.|