Guy's I thinking of doing another run of our now, old, S100 bus IDE/CF card board. There are probably close to 150 of them out there by now.
It's described here:-
Hard to believe but the first board was back in 2010!
While the V2 board seems to work fine for most people, there may be some things "not quite right" with the design for high bus speeds around 10MHz and with fast CPU's like the 80386 and with multi-sector reads with MSDOS etc.
I decided the time was right to fine tune the board for another run, a V3 version. There are a few things I wanted to do.
1. I do not want to change the basic 8255 driven circuit and all the software I and others have over the years written for the board. Sure if I were to do it all over again I would probably have done it different using perhaps a faster Zilog PIO or an onboard fast fully dedicated Z80 (as for our ZFDC board) or Propeller etc. The NEC or OKI 82C55-2’s are dirt common and seem to be able to handle anything the CPU sends to them.
2. I want to hand lay down broad power traces to all the boards IC’s for more even power distribution – particularly to the power hungry HEX displays.
3. I have inserted a trace “Keep out Area” on the front of the board so there is no danger of the IDE adaptors touching a critical trace.
4. I added a single TO-3 V regulator (e.g. 78H05’S) capable of delivering high currents without overheating the board locally. Yes I know we should be going to the switching regulators, but this is often a first board for builders, wanted to keep it simple.
5. However I did bend the rules a little and add one 22V10 GAL. This greatly simplifies the board and really speeds up the port addressing and the potential drive select/reset issues some were having. I realize not everybody is familiar with GAL’s. For those people and beginners I will supply the pre-programmed Lattice 22V10 GAL. Will of course supply the PALASM code for others. Again these GAL’s are fairly common (Jameco #39159 for the 15ns variety).
6. I have switched over to using a 74LS00 (instead of the OC 7403’s) for the critical RD/WD circuit. This is based on (Roger & others) observations. Still a bit worried about this, but it’s a prototype can easily add pull-ups and a 7403.
7. People should be able to simply switch IC’s from the old board to this new one. Only a new GAL IC is required.
8. Last but least I relabeled much of the Silk Screen to be more relevant. For example placing IC numbers above their pin locations.
I’m attaching a suggested schematic and a picture of the proposed V3 board. Could people take a look at it? Any suggestions etc. will be gratefully received. Dave in particular I would really appreciate your input. You have a keen eye for detecting potential issues and know this board well. I have added my complete working KiCAD file folder at the very bottom of the page of the above URL for anybody that has the time to look.
IDE Board V3 Prototype Schematic.pdf
Description: Adobe PDF document
IDE Board V3Prototype.JPG
Description: JPEG image