"mdnttrain@aol.com" wrote:
> I tend to agree with David on the usefulness of having a POST, the
> functional core concept, and the incremental adding of tested hardware
> to this core until the system is fully up. That's exactly what I'm
> trying to do.
> I am running an Imsai front panel... but that's of no efficient use
> when trying to ascertain whether all my RAM chips are good upon
> startup.
> I have managed thus far to locate the source code to a Heath H17 ROM
> -- which has a memory test in it.

If you have the Heath documentation, look for a tiny little memory test
program they provided with the H8's and H89's. It's a RAM test program
so short that you can key it into your front panel or monitor. The test
routine moves itself up 1 byte, and executes itself. Thus it "walks" to
the top of RAM, outputs something to indicate success (lights a front
panel light, beeps the terminal), and repeats from 0.

It's not a very thorough test, but it does catch one kind of error
peculiar to the Z80. The Z80 requires the shortest memory access time
for an instruction fetch; so if all you do are data reads and writes,
you will miss memory that is good but too slow to execute a program

> The rom-based PC Bios was revolutionary in how it abstracted the
> hardware from the OS...

Err... weren't there already a huge number of machines that did this?

And... just like all the other computers, people soon found that the ROM
BIOS was limited and buggy, and so loaded their own drivers to replace
Ring the bells that still can ring
Forget the perfect offering
There is a crack in everything
That's how the light gets in -- Leonard Cohen
Lee A. Hart, 814 8th Ave N, Sartell MN 56377, leeahart_at_earthlink.net