[sebhc] H8 Tape interface debugging?

Dave Dunfield dave04a at dunfield.com
Sun May 16 15:15:56 CDT 2004

Hi Guys,

I fired up my H8 today, and for the first time connected a tape recorder
and tried to load the software tapes.

The good news is that the interface appears to "mostly" work - it detects
the tape and walks through memory as it loads - everything looks right.

The bad news is that the only tape I could get to load was BUG-8. It
loads consistantly, while the other programs TED8, HASL8, BHBASIC all
fail. I've tried various tape volume levels and no joy yet.

At first I thought this might be because I have only a single 4K memory
board in my H8 - at least the manual I have says 4K, and there is only
one memory board, however looking at the SP which is initialized by PAM-8
suggests there is 8K (it's set to 077,377 = $3FFF, and since memory starts
at 040,000 ($2000) ... $2000-$3FFF is 8K - the schematic for the RAM board
calls it a 4k/8k board, so it looks like I have 8K after all.

I tried keying in the memory test from the beginning of the operation
manual, setting it for 8K, and it ran with no errors - so I'm pretty
sure there is 8K of functional RAM in there.

I also tried dumping memory out to the tape and restoring it. I was
able to dump/load a few small blocks, however if I try to dump/load a
large block, it always fails - looks like something is drifting (it's
worth noting that Bug-8 is the smallest of the Heathkit images).

Anybody got any hints/suggestions/experiences with debugging the
H8 tape interface?

dave04a (at)    Dave Dunfield
dunfield (dot)  Firmware development services & tools: www.dunfield.com
com             Vintage computing equipment collector.

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