Nice and simple 65816 upgrade for original 800?

[Kyle22]

I did this, and it works fine with everything I tried, except of course software written using illegal opcodes, same as the 65802.

 

The unusual part is that while it works, I discovered one side effect.

 

Incognito almost if not always forgets its settings, but the clock is always correct.

 

I have replaced the Lithium cell, and no change.

 

It's no biggie because I put the 65802 back in.

 

I just wanted everyone to know.

[JamesD]

...

John Harris made some instructional posts a few years back when the company he was associated with did a 65C816 system. I think the memory move he posted was only 21 bytes vs. the ~40ish for a standard 6502. I know just using the 65C02 instruction set allows you to write ~5% tighter code. Overall the lower current, reduced code size and resultant faster execution just for adding a jumper and $10 processor seems like a real win. I think B&C has/had some of the old style boards for people that want to revert their 800 back to 6502B/65C816 for ~$15.

...

This is the macro I used for my 64/80 column graphics text screen scroll. It's slower than an unrolled loop copying 16 bits at a time..

This is for the CA65 assembler.

 

;*********************************************
;* 65816 support
;*********************************************
.if Use65816 = 1
.P816
;Memory Move Negative.  Move from hi to lo address.
;Memory is moved at the rate of seven clock cycles per byte.
; MVN increments the X and Y registers, and decrements A
; The non-maskable interrupt (NMIEN) must be disabled on the Atari unless
; you have your own interrupt handler to deal with 65816 code
;*********************************************
.macro	MOVEMEMN	SourceAddress,DestAddress,BytesToMove,SourceBank,DestBank
	SEI
	clc
	xce					; native mode
	rep	#$31				; set A, X, and Y to 16 bit, clear carry
.A16						; Tell assembler Accumulator is 16 bit
.I16						; Tell assembler Index registers are 16 bit
	LDX	#SourceAddress			; The source address for the memory move
	LDY	#DestAddress			; The destination address for the memory move
	LDA	#BytesToMove-1			; The number of bytes we want to move + 1 because MVN needs it
	MVN	SourceBank,DestBank		; RAM banks, should be 00,00 on 64K system
;	sep	#$31				; set A, X, and Y to 8 bits, set carry
	xce					; emulated mode
.A8						; Tell assembler Accumulator is 8 bit
.I8						; Tell assembler Index registers are 8 bit
	CLI
.endmacro
.endif

I also had to disable the Atari non-maskable interrupt before entering 16 bit mode.

 

	LDA	#0				; turn off ATARI non maskable display interrupts for 65816
	STA	NMIEN

Edited February 5, 2017 by JamesD