hi all,
After 40+ years I revived my Electors Junior Computer and now I'm running BBC Basic on it![:-)]( "Smile")
To achieve this I did some "minor" changes to the board: I added a small piggyback board with a 128K ram chip in stead of the 2 pieces 2114, an extra address decoder 74LS145 to decode 8 blocks of 8K, of which the top 2 outputs are connected to the EX input on the Junior. The other 6 blocks are connected to the /CS1 of the ram giving 48K. Also connect PHI2 to CS2. So now the original Junior hardware is addressed at E000 ..FFFF (was 0000-1FFF)
In the original Junior monitor I changed all references of $1xxx to $Fxxx. So the monitor is at $FCxx in stead of $1Cxx and 6532 RIOT is now at $FAxx.
I wrote a "MOS" which I upload to $D000 in ram via the standard serial routines in Juniors PME (1200 baud, 7 (!) bits) on PA7 and PB0. In my MOS I communicatie via the same ports but now at 9k6. In the MOS I implemented XMODEM (thanks Joerg Walke), callable via OSFILE which replaces the tape COS and some OSBYTE/OSWORD/OSCLI and OSFILE stuff. The original references at $FFF4 (OSBYTE), $FFEE (OSWRCH) etc I have changed to $DFF4, $DFFE etc, at least as long I keep the original Junior monitor in the eprom. In Basic2 I changed these same references.
So far so good, Basic runs. Even sound, also bit banging on the PB7 output of the 6532, with a conversion table from the BBC pitches to uses timing. No interrupt though, since the timer in the RIOT disturbs the bit banging timing for IO. Maybe add an 6850 ACIA under interrupt, then this problem is solved.
So far this update, quite satisfactory already but there is of course a lot to improve!
Bas
After 40+ years I revived my Electors Junior Computer and now I'm running BBC Basic on it
To achieve this I did some "minor" changes to the board: I added a small piggyback board with a 128K ram chip in stead of the 2 pieces 2114, an extra address decoder 74LS145 to decode 8 blocks of 8K, of which the top 2 outputs are connected to the EX input on the Junior. The other 6 blocks are connected to the /CS1 of the ram giving 48K. Also connect PHI2 to CS2. So now the original Junior hardware is addressed at E000 ..FFFF (was 0000-1FFF)
In the original Junior monitor I changed all references of $1xxx to $Fxxx. So the monitor is at $FCxx in stead of $1Cxx and 6532 RIOT is now at $FAxx.
I wrote a "MOS" which I upload to $D000 in ram via the standard serial routines in Juniors PME (1200 baud, 7 (!) bits) on PA7 and PB0. In my MOS I communicatie via the same ports but now at 9k6. In the MOS I implemented XMODEM (thanks Joerg Walke), callable via OSFILE which replaces the tape COS and some OSBYTE/OSWORD/OSCLI and OSFILE stuff. The original references at $FFF4 (OSBYTE), $FFEE (OSWRCH) etc I have changed to $DFF4, $DFFE etc, at least as long I keep the original Junior monitor in the eprom. In Basic2 I changed these same references.
So far so good, Basic runs. Even sound, also bit banging on the PB7 output of the 6532, with a conversion table from the BBC pitches to uses timing. No interrupt though, since the timer in the RIOT disturbs the bit banging timing for IO. Maybe add an 6850 ACIA under interrupt, then this problem is solved.
So far this update, quite satisfactory already but there is of course a lot to improve!
Bas
Statistics: Posted by basdejong — Sat Jun 22, 2024 11:45 pm