The display interface

Note : if anyone reads this and thinks I've done something obviously wrong, please tell me - I'm not really an electronics guy.

Atari Cosmos PCB, track side

This is probably the single most useful image I have. It not only shows some of the connections and wiring but gives hints as to others. This is a single layer single sided PCB, so tracks must go in the direction of things that use them - or there needs to be a corresponding wire on the top side of the PCB.

COP444 Pinout

So, the first and most obvious thing is this is the flipside of the COP444. It's pinout is on the left (hopefully ....).  Bearing in mind it is upside down - e.g pin 1 is the lower right pin (you can see the 1) we can see the lines D0-D3 and G0-G3 on the top right of this PCB.

Seven of them, representing the seven columns (or seven segments) are connected to resistors (that go over the ATARI INC label) and straight into the Display Connector.

It is highly likely that these are the connectors to the display columns (think of it as a 7x6 array + the 7 segment displays). Nothing else makes sense.

I don't know how the wiring is done, but for the sake of programming sanity it is likely to be G2 G1 G0 D3 D2 D1 D0. It might not be - sometimes designs are done for ease of wiring and it's sorted out in the software - but there are so many complex wires in the display board it doesn't seem like it would matter and when you are cramming 8 games into 2k of 4 bit code then that's your low resource.

G3 is not connected in the same way - this is the track that heads off to the top left corner for a bit, and I think, connects to the track between the words www and atari (I must give references for these pics), after which it heads off left.

This, I think has to be the line that selects which of the two holographic displays to be used (the Cosmos has an overlay for the LEDs and can programmatically display one or the other). It's off in the right direction, and it is not the same functionality as the other G and D ports.


On the bottom side, mostly are the L-lines. These are bidirectional I/O lines. The

LED Driver circuitry using transistors

first two L0 and L1 which are the two most extreme left pins are connected to 0V via pull down resistors. The rest of the L lines seem to head off left and top left.  This direction, and some resistors, and the fact that there are conveniently 8 of them, suggests that these are the row drivers - there are 6 rows plus two seven segment displays. There are 8 transistors in the top right of the board (looking at the component side) and resistors and transistors that suggest this arrangement shown on the right (hopefully) where A0-A6 are G + D and B0-B7 are L0-L7.  Again, I do not know which row or display is connected to which L-line.  I am working on the principle that the 6 LED Rows are L0-L5, L6 is the left digit and L7 the right digit, and the segments are in standard form, but actually this doesn't matter as it'll be driven from two lookup tables.

This doesn't leave much. The two clock inputs, RESET, the power lines,  the four input lines IN0-3 and the Serial I/O connections to the Sound Microcontroller. (SK SO SI).

There's two outstanding issues. First is the game selector , and second is the keypad layout. This latter is, well .... interesting.

Irrelevancy: The COP444 has an "OMG" instruction, which is coincidential (it's too old) - it outputs a Memory Nibble to the G port, which belongs with HCF and SEX. I'm sure they weren't accidents :-)