[Coco] 64K ROM to RAM programs - where did this one come from?

[Dave Philipsen]

Or maybe just get rid of the whole push/pull cc thing and finish off with a andcc #$af. 



> On Dec 14, 2021, at 3:31 PM, L. Curtis Boyle <curtisboyle at sasktel.net> wrote:
> 
> You could shrink it by a byte with 4032 being a PULS CC,PC instead. :-)
> 
> 
>> On Dec 14, 2021, at 3:24 PM, Allen Huffman <alsplace at pobox.com> wrote:
>> 
>> Using a Motorola 6809 Emulator I found online (which turns out to be the Xroar site):
>> 
>> http://6809.uk
>> 
>> …I was able to convert the DATA statements from the ROM to RAM program in to “fcb” constant bytes…
>> 
>> start:
>> fcb $34,$01,$1A,$50,$10,$8E,$80,$00
>> fcb $B7,$FF,$DE,$EC,$A4,$AE,$22,$EE
>> fcb $24,$B7,$FF,$DF,$ED,$A1,$AF,$A1
>> fcb $EF,$A1,$10,$8C,$FE,$FC,$25,$E8
>> fcb $10,$8C,$FF,$00,$24,$0C,$B7,$FF
>> fcb $DE,$EC,$A4,$B7,$FF,$DF,$ED,$A1
>> fcb $20,$EE,$35,$01,$39
>> 
>> …then “assemble” it and look at the output in the emulator:
>> 
>> 4000:    34 01             PSHS CC
>> 4002:    1A 50             ORCC #$50
>> 4004:    10 8E 80 00       LDY #$8000
>> 4008:    B7 FF DE          STA $FFDE
>> 400B:    EC A4             LDD ,Y
>> 400D:    AE 22             LDX $02,Y
>> 400F:    EE 24             LDU $04,Y
>> 4011:    B7 FF DF          STA $FFDF
>> 4014:    ED A1             STD ,Y++
>> 4016:    AF A1             STX ,Y++
>> 4018:    EF A1             STU ,Y++
>> 401A:    10 8C FE FC       CMPY #$FEFC
>> 401E:    25 E8             BCS $4008
>> 4020:    10 8C FF 00       CMPY #$FF00
>> 4024:    24 0C             BCC $4032
>> 4026:    B7 FF DE          STA $FFDE
>> 4029:    EC A4             LDD ,Y
>> 402B:    B7 FF DF          STA $FFDF
>> 402E:    ED A1             STD ,Y++
>> 4030:    20 EE             BRA $4020
>> 4032:    35 01             PULS CC
>> 4034:    39                RTS
>> 
>> I can now see why it is larger. Instead of copying a byte at a time, like the Frank Hogg version, it copies 6 bytes at a type by loading them in to three 16-bit registers (D, X and U).  That means it is 6 times faster, I guess ;-)
>> 
>> But, what is going on at $401A with the compare against address $FEFC followed by a compare against $FF00?
>> 
>> 
>> 
>> -- 
>> Coco mailing list
>> Coco at maltedmedia.com
>> https://pairlist5.pair.net/mailman/listinfo/coco
>> 
> 
> 
> -- 
> Coco mailing list
> Coco at maltedmedia.com
> https://pairlist5.pair.net/mailman/listinfo/coco