Recently I was bringing up an Apple 1 and I did the first thing I always do to do an initial checkout, which is run the Test Program from the Apple-1 Operation Manual. This is a very simple program that runs a loop that counts from 0x00 to 0xFF and prints each byte as an ASCII character. Here is the program:
0000 LDA #0
0003 JSR ECHO
0008 JMP $0002
This time when I brought up the Apple 1 I saw the following output:
The last time I had run this program, I had run it on an emulator and seen the following:
Remembering how the output looked I thought there was a problem with my Apple 1. After further investigation I found the answer in the Apple 1 schematics.
It turns out that character output is tied to RD6 or RD7. This was overlooked in every Apple 1 emulator that I have looked at.
Tonight I’ve posted the first release of my version of the pom1 Apple 1 emulator. This emulator needed a number of modifications in order to turn it into an applet, but it is now in working form. Next steps are to add reset and clear functions, then try to get BASIC running.
Visit the Emulator page to see it in action!