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Wanted Replacement PAL Chip CorComp FDC 1985 rev A U12

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Doug, spotted two errors on the lovely PCB layout:

 

(1) The trace to PAL U12 pin 3 isn't connected to anything - I assume it needs a green trace going vertically down to A1 on the PEB edge connector.

 

(2) I can't see how the ground trace running round the left / top / top-right of the board is connected to the ground trace at the bottom-right of the board. Is there a ground trace missing round the corner just below the floppy connector? Or maybe to the GND pins at the left end of the PEB connector?

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Equations for PAL U12 attached, as far as I can work out. The address decoding looks convincing.

 

Doug, are you able to program a GAL (when you have time) and run it through your reader to see if you get the same data? I can create a JEDEC file if needed.

 

post-31406-0-57712200-1552405458_thumb.gif

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Posted (edited)

Another error or two on PCB layout, and I can't edit my earlier post ;-/

-- 74LS123 towards top right of board. No connection to pin 16 (Vcc). Should probably connect to the decoupling cap just above it.

 

-- 74LS11 towards bottom left of board. No connections to pins 1, 3 ,5 (a wiring error around here I think - the 2Y output on pin 6 is shown as connected to pin 2, which is connected to A13 from the PEB). (Also pins 8, 9, 10, 11 but this gate is possibly unused.)

Edited by Stuart
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Another error or two on PCB layout, and I can't edit my earlier post ;-/

 

-- 74LS123 towards top right of board. No connection to pin 16 (Vcc). Should probably connect to the decoupling cap just above it.

 

-- 74LS11 towards bottom left of board. No connections to pins 1, 3 ,5 (a wiring error around here I think - the 2Y output on pin 6 is shown as connected to pin 2, which is connected to A13 from the PEB). (Also pins 8, 9, 10, 11 but this gate is possibly unused.)

Thank you - all valid catches!

 

::curses in boolean::

 

Points in reverse order:

74LS11 does in fact have one unused triple 3-in AND (pins 8-11). Pins 1, 3, 5 are floating - I learned never to design this way (assume "1" or high float if unconnected), but didn't want to start ragging on creator as some routing in this design leaves a lot to be desired.

74LS123 was connected as you state and I can only blame myself for somehow highlighting it in edit when I deleted something else so it went poof.

Ground plane around right center of board should have continued as you surmise. Oversight on my part.

Orphaned via above PEB card edge connector should be connected straight down to finger pad ... again, an errant fat-finger deletion during editing.

 

I also can't edit my previous post to replace the ZIP attachment, so I'll reattach it here with all the corrections and hope everybody finds this reply and downloads it again - my apologies to everybody's bandwidth/time.

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Equations for PAL U12 attached, as far as I can work out. The address decoding looks convincing.

 

Doug, are you able to program a GAL (when you have time) and run it through your reader to see if you get the same data? I can create a JEDEC file if needed.

 

attachicon.gifPAL U12 Connections and Equations UNTESTED.gif

 

Thanks and I agree with U12 performing bulk of master selection logic - had hand crammed about half of the reduced output file when I started to see the patterns, just so time consuming.

I don't have a PAL/GAL programmer (WANT) - eBay prices I've checked are for all used *as is*, discontinued programmers and priced too high for my budget.

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Non-subscribers have a limited time window in which to edit posts in "normal" forums. Since you are actively developing this, I can move this thread into Dev and you can there edit posts for a longer period of time.

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Non-subscribers have a limited time window in which to edit posts in "normal" forums. Since you are actively developing this, I can move this thread into Dev and you can there edit posts for a longer period of time.

 

That would be great if it meets the needs of the community, thank you. I don't want multiple revised attachments that people have to cypher which one is the most current. :skull:

I'm pretty sure I am a subscriber though, at least I have to sign in with a user/pass (figured forums had set time limits for editing after original post/reply).

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Posted (edited)

Does anyone have a PAL programmer? Most USB programmers will do GALs, but there isn't a GAL equivalent for the PAL12L6. Or someone fancy knocking up a little PAL12L6--> GAL16V8 adaptor board?

 

*** Correction - looks like a GAL16V8 can directly replace a PAL 12L6 ***

Edited by Stuart

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Thank you - all valid catches!

 

::curses in boolean::

 

Points in reverse order:

74LS11 does in fact have one unused triple 3-in AND (pins 8-11). Pins 1, 3, 5 are floating - I learned never to design this way (assume "1" or high float if unconnected), but didn't want to start ragging on creator as some routing in this design leaves a lot to be desired.

74LS123 was connected as you state and I can only blame myself for somehow highlighting it in edit when I deleted something else so it went poof.

Ground plane around right center of board should have continued as you surmise. Oversight on my part.

Orphaned via above PEB card edge connector should be connected straight down to finger pad ... again, an errant fat-finger deletion during editing.

 

I also can't edit my previous post to replace the ZIP attachment, so I'll reattach it here with all the corrections and hope everybody finds this reply and downloads it again - my apologies to everybody's bandwidth/time.

 

Yikes! They're leaving inputs floating? Definitely no connections between adjacent pins directly under the socket?

 

Can you triple(!)-check one of the connections around the 74LS11 again when you have time, as it doesn't make sense. We have A13 coming onto the card through the PEB connector and that goes to the RAM pin 5 (A0), which is fine. It then goes to the LS11 pin 2 (1B input) which is fine. It then goes to the LS11 pin 6 (2Y output) which is NOT fine as this output will fight the A13 input coming onto the card. It then goes to the 9901 P2 and pull-down resistor, which I would expect to be driving an input somewhere.

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Yikes! They're leaving inputs floating? Definitely no connections between adjacent pins directly under the socket?

 

Can you triple(!)-check one of the connections around the 74LS11 again when you have time, as it doesn't make sense. We have A13 coming onto the card through the PEB connector and that goes to the RAM pin 5 (A0), which is fine. It then goes to the LS11 pin 2 (1B input) which is fine. It then goes to the LS11 pin 6 (2Y output) which is NOT fine as this output will fight the A13 input coming onto the card. It then goes to the 9901 P2 and pull-down resistor, which I would expect to be driving an input somewhere.

 

Okay, embarrassed I missed that. Took a cheapy USB microscope shot top/bottom so you can see the traces. There is an additional tie on the bottom between 74LS11 pin 1 and 2.

I'm going to stand by my comment of Pin 5 and the other three inputs to the unused gate still floating.

 

On your second point, I warmed up my ohmmeter in continuity mode and found the upper hidden trace should be routed down to Pin 3 rather than Pin 2 (which indeed would fight PEB A13 with Pin 6's output).

I did a lot of "does this make sense to me" when copying the layout, obviously I missed one (I hope that was the only errant trace because that wastes people's time).

 

Corrected and revised ZIP attached. Keep errors coming - I don't mind ... just feel stupid.

As suggested about managing attachment settings, I've removed previous versions of the file in messages.

post-48993-0-95949800-1552422235.jpg

post-48993-0-60896300-1552422244.jpg

Corcomp_FDC-RevA.zip

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I don't mind ... just feel stupid.

 

Don't be! That's a huge amount of work you've done. ;-)

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Exactly that--I am really glad you were able to take the time to do this. Errors will creep in, it is part of the deal. Correcting them is half the fun of the project. . .

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Equations for PAL U6 attached, as far as I can work out. I think I might have the AND and OR symbols in the equations the wrong way round - they probably need a bit more work to tidy up the syntax.

 

post-31406-0-99776900-1552433206_thumb.gif

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I have a EPROM/EEPROM/PAL programmer : Here is the list of the PLDs it can read/write:

20 pins: 10H8,12H6,14H4,16H2,16C1,10L8,12L6,14L4,16L2,16L8,16R8,16R6,16R4,16X4
24 pins: 12L10,14L8,16L6,18L4,20L2,20C1,20L10,20X10,20X8,20X4,20L8,20R8,20R4

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That would be great if it meets the needs of the community, thank you. I don't want multiple revised attachments that people have to cypher which one is the most current. :skull:

I'm pretty sure I am a subscriber though, at least I have to sign in with a user/pass (figured forums had set time limits for editing after original post/reply).

 

The kind of subscription that Alan (@OLD CS1) is alluding to and that affords extra time for editing posts, more messages, more uploads than regular subscribers is a paid subscription, which is how this marvelous site is supported. You can see more detail here.

 

...lee

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