I've just tried a little circuit on my Replica 1 using a 74LS377 and some LEDs to test something else I want to build. I tied the 377 enable to /A000 from the Replica 1 expansion - this signal goes low when I write to any Axxx address. Then I simply connect the data bus from the 6502 to the inputs ...

If your rand() implementation is not too expensive, I'd also suggest just looping until acceptable (though if the range is narrow, consider the best 'n' bits only - e.g. the high bits if you're using a simple LCG algorithm).

The % operator is fundamentally a division, and that's slow on the 6502 ...

Thanks for the many and varied suggestions!

Ken

Hi,

I thought I'd ask for suggestions about adding sound to my 6502 SBC (a Replica 1). Specifically, I want it to be a fairly minimal board that I could connect to the expansion interface. This is really just to amuse my kids, so it doesn't need to be polyphonic - even just a few notes would do ...

Some of you may remember a couple of my earlier threads asking for some programming advice, well, building this assembler was the reason. I bought one of Vince Briel's Replica 1 kits earlier this year, and wanted to be able to program it in assembly language directly. So I taught myself 6502 ...

Presumably he's cross-compiling.

Nice - thanks. Not only short and clear, but also avoids using X, so you've saved me quite a few bytes there.

Ken

Hi,

I need to add a signed 8 bit number (in zero page location TEMP1) to a stored 16 bit number (in zero page locations LVALL,H). Below is my current method. I was wondering if anyone had any suggestions or improvements.

ADD16X
LDX #$00
LDA TEMP1 ; signed 8 bit number
CMP #$00
BPL .CONT
DEX ...

Most entertaining thread ever. I don't think I'll ever enjoy assembly programming on any other processor as much as on the 6502. What fun.
I've certainly enjoyed it, and learnt a lot - which was of course the idea. I'm writing an assembler to use with my Apple-1 replica, and the problem comes from ...

Looks like it.

This is a good way for me to learn I think.

Hmmm, sorry if I'm misunderstanding something (as I said, I'm fairly new to 6502 assembly), but your last two instructions - the AND and ORA won't change temp, only A. So if the result is in temp, you could stop earlier!

I understand what you're doing. You put 00000100 in temp, and then copy the ...

Thanks very much - that does help. I think you mean result in A though.

Ken

Hi,

I'm relatively new to 6502 assembly, but since I built a Replica-1 (Apple-1 clone) in January, I've been doing quite a lot. What I need to do at the moment, is to transform a byte of the form "XXXY YYZZ" to "001Z ZXXX", and various similar operations. Now I can obviously do this with various ...