Smonson's slow H4 build

[Smonson]

I finally assembled the board representing the schematic above... only a few years late.

It worked first time and boots up 2.06 on the H4 (yay), but 1.04 crashes after about a second. I guess that's progress!

I'll poke around some more on it soon to figure out what isn't working.

completed-board.jpg (68.52 KiB) Viewed 6171 times

running-206.jpg (59.12 KiB) Viewed 6171 times

[Smonson]

It worked first time and boots up 2.06 on the H4 (yay), but 1.04 crashes after about a second. I guess that's progress!

My mistake was that I connected the ROM selector from the GLUE, which I have been calling ROM2, to that pin (ROM2). But actually this is not ROM2 at all because ROM2 only selects the bottom 64K of ROM space (everyone calls this ROM2 for some reason). I inherited this from @thomasM74 H5 build thread when I was looking for a good place to attach the wire.

The real place to attach it is pin 4 of the nearby AND gate which is the output to OE on the ROM socket. The similar arrangement on a real ST goes to CE on ROM sockets LO-0 and HI-0 to achieve the same goal.

Rather than rip the pad off the AND gate I actually attached it directly to the pin on the PLCC44 socket, underneath, and ran the wire through one of the power connectors. Woohoo, it works for 1.04 now as well as 2.06!

[Smonson]

Well, haha, I made another ROM decoder up to install in my other STFM. The good news is that it worked.

But the bad news is something that I probably should have seen coming a mile away.

not-fitting.jpg (196.62 KiB) Viewed 1659 times

Ahhh well. I'll just have to make an alternate version with the CPU further back.