[sebhc] 64K memory

Dave Dunfield dave04a at dunfield.com
Mon May 17 17:31:47 CDT 2004

Hi Lee,

>> This looks like it would be dead easy to throw into the emulator.
>> What I would need is:
>>   - Detailed documentation on the commands
>>   - Binary dump of the ROM
>>   - A bootable disk image for testing.
>> Anyone want me to persue this?
>Dave, I'd be happy to photocopy what I have and send it to you. Just
>send me your address (privately, if you like).

Thanks - I'll send you my address.

>However, I never really liked the H47. It was cheaply madel, and
>unreliable (what kind of nitwit makes an 8" disk drive out of molded
>plastic and sheet metal). They were single-sourced, so when it broke,
>that was the end of the line.

These mechanical issues are not a concern in the emulator, as this will
be a software only implementation. It will use a file on the PC to
emulate the disk drive.

I thought it might be interesting because it sounds as if the software
interface is fairly simple, and it might be very easy to add it in to
my emulator, which would give us a bootable disk.

>I would think that one of the other options mentioned earlier would be
>preferable. For example, using the H8's RS-232 or cassette serial ports
>to communicate with the PC.

Although this does not apply to the emulator, it is something that I have
been thinking about.

It would take very little to modify the H8-5 board to perform direct upload
with the PC through the cassette port - this would allow you to use "digital"
means without having to constantly having to change the "interchange" switch
(which requires you to leave the top off).

Assuming your chips are socketed, you could do this without damaging the H8-5
board at all (This is important to me, as I believe in preserving these machines
as much as possible).

All you need to do is build a little RS-232 driver board (MAX-232?) and switch
the IC123 RXD/TXD connections to go to this board. You could also jumper it to
run at 9600 bps from the console serial baud rate selector.

You can disconnect the existing tape interface just by lifting a couple of IC
pins, then tack on wires to the level convertor board, and you should be all
set to go "high speed" digital.

>Longer term, I am attracted to the idea of making a proper disk
>controller board for the H8. Since the old WD1797 chips are so scarce,
>and Heath already (sort of) supported SCSI with the H67, maybe the way
>to do this is by implementing a SCSI board, which could plug into a hard
>drive from an old Mac or PC, or a 1.44meg floppy drive from a Mac (they
>were SCSI), or even a PC with SCSI card (two SCSI devices can exchange
>data directly).

Agreed, we could do our own ROM to make this as transparent as possible.
Another possibility for the hard drvie is IDE - I've used IDE drives in
a couple of small embedded systems, and they are really quite easy to talk

Btw, does anyone have the specs for a disk controller ROM - what functions
must it provide to be able to boot and run the standard OS's?

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

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