CMT 4 ROM Board

discussion of games, software, hardware & emulators relating to the Acorn Atom
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simoni
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CMT 4 ROM Board

Postby simoni » Sat Jul 01, 2017 4:45 am

There was a CMT 4 ROM board mounted in the Acorn Atom that I recently restored:

IMG_20170625_165556.jpg


As you can see in the picture, one of the ICs has been scratched to hide the markings. Since I like the 'originality' of the hardware I decided to restore it too and also reverse engineer the circuit. The 'mystery IC' is a SN54LS75. Attached are 600 DPI scans of the PCB (both sides), the single-sheet user manual and a KiCAD schematic of the board (untested - drawn mainly to help identify the unmarked IC).

I'm including it all here in case someone else finds one of these boards (I can't find any references to them via Google).

/Simon
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CMT ROM Board Schematic - Acorn Atom.pdf
(60.01 KiB) Downloaded 28 times
CMT ROM Board Manual - Acorn Atom.pdf
(55.95 KiB) Downloaded 27 times
PCB Side 2.png
PCB Side 1.png
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Multiwizard
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Re: CMT 4 ROM Board

Postby Multiwizard » Sat Jul 01, 2017 6:50 am

Hi Simon,

nice board... :D

Several years ago one of the Atoms I received also had a (for me) unknown switchboard inside... :-k

Last year I build it in my Acorn ABM... 8)


Greetings, Wim... :-)
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12440427_10206150001885287_2495387690557877165_o.jpg
12888663_10206150002925313_503429329154914119_o.jpg
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Re: CMT 4 ROM Board

Postby simoni » Sat Jul 01, 2017 7:03 am

Hi Wim

I did finish restoring the board; but I didn't think to post any pictures of it after the work was done :)

Here's the top-side:

IMG_20170701_085440.jpg

And here's the underside:

IMG_20170701_085511.jpg

It's designed to sit directly in the IC24 socket with a single wire to the R/!W line of the program RAM. I haven't put it back in the Atom yet as I'm still working on the machine (just some minor testing to go).

The design of the board you posted is certainly interesting; I like the big semi-circle of tracks between the IC rows, looks funky even if it breaks the golden-rule of keeping IC orientation constant ;)

/Simon
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Multiwizard
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Re: CMT 4 ROM Board

Postby Multiwizard » Sat Jul 01, 2017 7:10 am

Nice restoring... :D

Is it me or did you turn the four 24pin sockets 180 degrees?


Greetings, Wim... :-)
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Re: CMT 4 ROM Board

Postby simoni » Sat Jul 01, 2017 7:20 am

Is it me or did you turn the four 24pin sockets 180 degrees?


The original sockets had rough edges at the bottom (where the plastic was snapped from the mould) which looks a little like a orientation tab, but it's not. On the PCB you can see the little '1' markers showing the correct orientation. The new sockets are the right way round; and much easier to see the marker :)
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Re: CMT 4 ROM Board

Postby daveejhitchins » Sat Jul 01, 2017 7:26 am

Multiwizard wrote:Is it me or did you turn the four 24pin sockets 180 degrees?
No, they're OK, pin 1 is marked - So it's you :lol:

Dave H :D
Parts: UM6502CE, GAL22V10D, GAL16V8D, AS6C62256A, TC514400AZ, WD1772, R6522, TMS27C512, AT28C256
Products: ARA II, ABR, ATI, AP6, MGC, AP5 . . .
For a price list, contact me at: Retro Hardware AT dave ej hitchins DOT plus DOT com
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Re: CMT 4 ROM Board

Postby Multiwizard » Sat Jul 01, 2017 8:23 am

daveejhitchins wrote:
Multiwizard wrote:Is it me or did you turn the four 24pin sockets 180 degrees?
No, they're OK, pin 1 is marked - So it's you :lol:

Dave H :D

Thanks dave :mrgreen: I knew something was wrong... :lol:


Greetings, Wim... :-)
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