warerat

This may come off as a little strong, but please, quit busting my balls this upgrade. There are several people on this forum that I have modified OS boards to give 64K 800XL (and one even has a 576K version). Rather than doubt my claims, a simple polite PM would suffice.

I do have an active work life outside of this forum, and it requires me to travel. I'm sorry if my schedule and the way I've implemented the design (read: Facaui) does not meet your criteria. I would like nothing more than to mass produce it, but I cannot at this moment. Not saying that it will never happen, but the way I've implemented it to be an all-in-one solution and the constraints of the 800 is a little more involved than the skill set of most hobbyists.

Please correct me if I reading you wrong, but to modify an OS board (or Ramrod) to provide minimal 64K 800XL compatibility (with RAM under ROM) can be achieved easily and if it placates the community I will do a write up.

orpheuswaking, on Thu Jun 16, 2011 6:28 PM, said:

My personal favorite is HDSC from drac030: http://drac030.krap....parta-pliki.php

Faicuai, on Tue Jun 14, 2011 7:28 PM, said:

The stock OS board is designed to take custom mask ROMs with extra chip selects that don't exist on EPROMs so you don't need additional external decoding circuitry.

My advice is if you don't want to redesign the OS board, design a piggy-back board that plugs into the the ROM socket that swaps pins and provides the logic to further decode the chip enable for an EPROM, or perform the decoder circuit modification for an EPROM, don't plug in the wrong chip and just to use a mask ROM that the socket is wired for.

fibrewire, on Tue Jun 14, 2011 10:25 PM, said:

It is none of those. It is a custom mask ROM with two active-high and one active-low enable.

Faicuai, on Mon Jun 13, 2011 7:06 PM, said:

The FP ROM and 2716 EPROM have completely different pinouts. It's even a stretch to say that 2532's would work in place of these because it's certainly not true in the case of the OS board.

Can it be made to work? Sure.
Piggyback another 74LS138 on top of the one at Z401. Bend up all the pins except 4, 6, 8, 16-- these are soldered to the 'LS138 below. Connections for top 'LS138: Connect pins 2 and 3 to pin 8, connect pins 4 and 5 together, connect pin 5 from the bottom 'LS138 to pin 1 on the top 'LS138.

Connections for EPROM: Pull it out and bend up pins 18, 20, 21 and plug back in. Run wire from pin 21 to pin 24 on EPROM. Connect pins 18 and 20 together and connect this pair to pin 14 of the top 'LS138.