Lord Crass

Still seems to work correctly with 1541. Tested 1571 with WS3 as well, detection routine working.

No, it's a parallel-only copier. The mirrored access it does at $6000 will cause it to crash if you have memory mapped there though. Memory at $8000 is no problem. Other parts the protection code are very specific to the drive ROM. Be sure you're using a 1541 and not a 1541-II. You also have to write-protect the disk or it won't load.

Confirmed working with 21 Second Backup v4.1, which does this: .8:0403 6C 01 64 JMP ($6401) - A:01 X:65 Y:00 SP:3d ..-B.IZ. 11213637 .8:a5c9 C4 52 CPY $52 - A:EC X:65 Y:00 SP:3d N.-B.I.. 11213642 .8:a5cb 49 56 EOR #$56 - A:EC X:65 Y:00 SP:3d N.-B.I.. 11213645 .8:a5cd 45 06 EOR $06 - A:BA X:65 Y:00 SP:3d N.-B.I.. 11213647 .8:a5cf 20 52 45 JSR $4552 - A:B4 X:65 Y:00 SP:3d N.-B.I.. 11213650 .8:4552 4C EC 66 JMP $66EC - A:B4 X:65 Y:00 SP:3b N.-B.I.. 11213656 .8:66ec FB 00 24 ISB $2400,Y - A:B4 X:65 Y:00...

Confirmed this fixes the problem with check I used in WS V3 cart. It also works as expected with Star Rank Boxing. Crashes if drive RAM enabled, works if disabled. I think one of the 21 Second backup copiers or the VG Datashack file copier also had some roundabout check for drive RAM, I'll see if I can dig that up and test as well.

Indirect indexed also behaves like absolute indexed. Returns what's in the prior page. Ran the openbus.prg with stock ROMs in NTSC C64C and 1541-II drive and it failed the majority of the time, highlighting a seemingly random byte as being wrong on each failure. Rough estimate is that it returned a green border maybe 20% of the time.

I edited my last comment as I forgot to test the case of crossing page boundary.

A few tests performed on a real 1541-II result in reading the high byte every time. Tried with load and compare instructions in all valid addressing modes. However, crossing the page boundary with an index mode results in different behaviour. LDX #$01 LDA $67FF,X (A = contents of $6700,X, which is $700,X when no RAM connected) LDA $68FF,X (A = contents of $6800,X or $68 when no RAM connected)

A few tests performed on a real 1541-II result in reading the high byte every time. Tried with load and compare instructions in all valid addressing modes.