Wozmon sends all characters to $D012 with the bit7 high.
Modern replicas and emulators print an 'H' when sending #$48 or #$C8.
I want to know if sending #$48 to $D012 in an original Apple-1 also prints 'H'.
If you have an original Apple-1, could you run this little program?
0000 A9 48 LDA #$48
0002 20 EF FF JSR $FFEF
0005 A9 C8 LDA #$C8
0007 20 EF FF JSR $FFEF
000A 4C 00 FF JMP $FF00
How many 'H's does it print?
On mine I get;
0000: A9H_\
Thanks!
Only one 'H' got printed, which means that sending $48 ('H', %01001000) doesn't print an 'H'.
So, it is mandatory to send bit-7 on: $01001000 OR %10000000 = %11001000 ($C8). Sending $C8 prints an 'H'.
But, now I have another question, why does it print an '_' before the '\'?
Hi,
I believe there's a problem in your program: the official entry point of WOZMON is not $FF00, but $FF1F (GETLINE).
In fact, there's a suspicious '_' in the output, which seems completely unrelated.
If you JMP to $FF00, you cause a re-initialization of the PIA and, somehow, this operation break up the printing of the last character that has been sent to it.
(TBH: it's not completely clear to me how this can happen because re-initialization should occur AFTER the printout - probably related to the DA/RDA lines).
Anyway, if you modify your code to:
0000 A9 48 LDA #$480002 20 EF FF JSR $FFEF0005 A9 C8 LDA #$C80007 20 EF FF JSR $FFEF000A 4C 1F FF JMP $FF1Fit will print two 'H's, as it should. (see picture below, taken from a 1:1 Replica).
Instead of returning to WOZMON, you can also try to JMP to $000A at the end of the program, to set an infinite loop:
000A 4C 0A 00 JMP $000Aand you'll get the two 'H's, too.
BR,
Claudio - P-LAB
20250522_200117[1].jpg
Wozmon outputs that when you transfer control to $FF00.
Claudio is right of course. Use the $FF1F re-entry point and it shows "HH". It is interesting that the emulator and the real hardware has different results on the $FF00 re-entry point though.
Thanks a lot! I understand it better now. :)
From wozmon
RESET: CLD ; Clear decimal arithmetic mode.CLI ; Disable interrupts.LDY #$7F ; Mask for DSP data direction register.STY DSP ; Set it up$7F is the ASCII DEL character, and the apple-1 shows an '_'. That explains why with JMP $FF00, when the board is already initialized, it shows an '_'.