Tuesday, May 1, 2012

Odds and Ends

I noticed a bug in the disassembler function of my JMON machine language monitor program. The destination address of branch instructions was wrong. I tracked it down to a conflict of page zero locations that was introduced in the last version when I added the memory test command. I fixed it and updated the code on github.com.

The remaining parts for my 16K memory board arrived so I can finally start assembling it. I confirmed that the EEPROM chips work when installed in the Multi I/O board. I also confirmed that the pin-compatible RAM chips work in the Multi I/O board. Watch for updates here as I build the board.

I recently blogged here about my port of the 2KSA assembler. I should mention that there are some other resident assemblers for the Apple 1 that are superior. Krusader comes in ROM with the Replica 1 and is excellent. Another option is the A1-Assembler which comes in ROM if you are using the Achatz A-ONE Apple 1 clone, or you can load it into RAM. I spent some time playing with it tonight and it is quite good.

When writing the ZOOP program I wanted a more flexible input routine than the Apple 1 BASIC INPUT statement. It always displays a "?" prompt, for one thing. In the end I ended up using it, but it got me thinking about my earlier machine language input routine. It only supports reading characters at a time and returning them as numbers via a PEEK command. I'd like to extend it to return strings.

Unfortunately, I can't think of an easy way to do it. There is no way Ican find in Apple 1 BASIC to convert a number to a string (e.g. an equivalent to the CHR$() function in most BASICs). A possible approach is to find where the BASIC string is stored in memory and write to it. I spent a little time on this tonight but didn't get any where.

Speaking of Apple 1 BASIC, some people have disassembled it. An upcoming task I plan to do is to get a disassembly of it to assemble and run again, and then see if I can make a few changes.

While one person reported to be playing it, no one has reported successfully completing my adventure game. Come on guys, is it really that hard? I hereby offer a prize (details to be determined) to the first person to successfully complete the game.

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