Thank you all for your answers!

First a clarification: the idea was that the DOS computer wouldn't have neither a video card nor a keyboard. Having no video card means that reading the video memory won't work. But having no keyboard has a consequence I didn't realize: most 8088 motherboards, the target I have in my mind won't boot because they stop, mentioning having not found a keyboard and the user has to press the F1 key.

Because of your comments I also realized that loading programs over IEEE means that at least INT13h has to be changed as well. This DOS computer won't have drives of his own so I cannot load MS-DOS and then some drivers that adjust things later on. So another solution popped up: I write my own BIOS. So far I'm only familiar with writing BIOSes for 8088 machines but that shouldn't be a problem; the idea was to use an 8088 machine anyway. I will start small: take a complete machine and first replace the INT 10h routine just to see if DOS still will start up. Then I will replace the INT 16h routine to see if DOS can be fooled/persuaded to accepts input not coming from a real keyboard. Next I will try to persuade the computer to boot from the IEEE port. And if all works, I'll remove the video card. Last step is to port the results into the BIOS.

For those who are not familiar with the IEEE bus, please have a look at: http://baltissen.org/newhtm/cbmhd.htm
Here you find a way to turn a PC into an IEEE device using a LPT port, a COM port and two ICs. And as this PC won't be a device but a master, I think just a LPT port will do. And this page will also answer the possible question how to attach mass storage devices to the whole. And my idea is more or less outdated, there exists much much smaller devices using SD cards: just google for PetDisk and PetSD. But mine looks more original :)

Thanks again for your comments!

Kind regards, Ruud Baltissen

On 4/28/21 12:13 AM, Ruud Baltissen wrote:
> But having no keyboard has a consequence I didn't realize: most 8088
> motherboards, the target I have in my mind won't boot because they
> stop, mentioning having not found a keyboard and the user has to
> press the F1 key.

Were the BIOS settings to not halt on no-keyboard not a thing with 8088
motherboards? All of my experience with such was Pentium or newer, so I
have no idea when that feature was added.

--
Grant. . . .
unix || die

Ruud,

Just a heads-up :

> Having no video card means that reading the video memory won't
> work. But having no keyboard has a consequence I didn't realize:
> most 8088 motherboards, the target I have in my mind won't boot
> because they stop, mentioning having not found a keyboard and the
> user has to press the F1 key.

IIRC without a video card installed you most likely won't even get that far,
but instead will be getting the motherboards boot-error beeps song. :-)

> For those who are not familiar with the IEEE bus, please have a look at:
> http://baltissen.org/newhtm/cbmhd.htm

[quote]
You need a PC that has (at least) one bidirectional LPT port,
[/quote]

Again IIRC, those old 8088 motherboards you are targetting did not have a
bi-directional printer port. At least, not like the current motherboards
have. Instead they just had open-collector pins with pull-up resistors
(more-or-less the same to the data pins of a(n Atmel) microcontroller). You
might want to double-check if the IEEE-488 hardware you want to attach can
handle that.

That ofcourse also means that the software on that website won't work for
those printerports and needs to be rewritten ...

Regards,
Rudy Wieser

Hallo Rudy,

> IIRC without a video card installed you most likely won't even get that far,
> but instead will be getting the motherboards boot-error beeps song. :-)

That's why I write my own BIOS: I will eliminate that part.

> Again IIRC, those old 8088 motherboards you are targetting did not have a
> bi-directional printer port.

Not on board, indeed. But any of those older LPT cards can be converted to bidirectional by cutting one line and soldering two others. In fact I prefer those cards with a LPT and a COM port on board: by piggybacking a 7406 IC on one of the others I have everything to create a full operational IEEE card. This trick won't work with some integrated ICs like the UM82C11.

Is this solution 100% electrical compatible with IEEE? No, the in and outputs of the unpowered ICs can disturb the communication of other IEEE devices.. That is why I always advice to disconnect the PC from the IEEE bus if not needed. When under power, I never had problems.

Kind regards, Ruud Baltissen

2021-04-28 at 11:01 -0600, Grant Taylor wrote:
> Were the BIOS settings to not halt on no-keyboard not a thing with
> 8088 motherboards? All of my experience with such was Pentium or
> newer, so I have no idea when that feature was added.

This was a common setup option on 386/486/Pentium mainboards, but not
on earlier hardware. The configuration options within a 8086 BIOS were
extremely limited (when there was a BIOS user interface at all).

Mateusz

Ruud,

>> IIRC without a video card installed you most likely won't even get
>> that far, but instead will be getting the motherboards boot-error beeps
>> song. :-)
>
> That's why I write my own BIOS: I will eliminate that part.

In that case the "no keyboard found" problem should be moot, as you can
eliminate it the same way. :-)

> But any of those older LPT cards can be converted to bidirectional by
> cutting one line and soldering two others.

Hmmm... I always understood that the old PC printer-ports where
bi-directional (no changes needed), just not in the same way as the modern
ones are.

But, you seem to have more experience with them than I have, so I'm going to
take your word for it.

Regards,
Rudy Wieser