Coleco Expansion Module #1 as a standalone 2600

[bigdcaldavis2k]

I am interested in turning my Coleco Expansion Module #1 into a standalone 2600 system, but I have no idea where to access the power and audio/video. I know I will need to add a switch to act as the on/off switch, but where exactly on the motherboard (or on the expansion connector) do you access these points? If you know, you can reply here or via email at either bigdcaldavis2k@yahoo.com or wvoutlaw2002@wmconnect.com

[joeybastard]

I have to ask this. Why?

 

This page has a CV schematic that might be of help:

http://www.atarihq.com/danb/files/colecovision.pdf

[Paul Slocum]

I have to ask this.  Why?

 

I investigated this before because it would make an awesome portable 2600. It's small and is laid out perfect for a D-pad and LCD screen to be installed. Plus you can usually get them pretty cheap. However it's not as easy as adding a battery and finding the A/V out:

 

http://www.atariage.com/forums/viewtopic.php?t=16460

 

-Paul

[joeybastard]

Ahhhh! That makes sense, a portable. Sorry for my cynical response!

[jsoper]

It's funny, I opened up an intv system changer for the exact same reasons a year ago. However, things were so spread out that it wasn't usable. The only way I could make a 2600 fit into a dreamcast controller was to handwire it all:

http://www.dreamwater.net/tech/abbibi/2600.html

 

Never did find a one-chip 2600 junior, man those things are rare.

John

[Godzilla]

wow that dreamtari is AWESOME. where can I buy one? :-)

[DanBoris]

I did a little research on the expansion module and here is what I found:

 

Looking at the expansion connector on the expansion module the top row of pins is number 1 to 30 going from right to left and the bottom row 31 to 60 numbering left to right.

 

Inputs to the Colecovision to the module:

 

13 Reset

60 -5v

1,2 Ground

58,59 +5v

57 +12v

45 CPU_CLK

 

 

Outputs from the module to the Colecovision:

 

11 BUSREQ (This is tied to ground in the module to disable the Coleco's CPU)

32 EX_VID_EN (This is tied to +12v in the module to enable the external video input to the coleco)

33 EX_VID (Video output)

31 EX_AUD (Audio output)

35 AUDCLK (Tied to ground in the module, probably to disable the sound chip in the Coleco)

39 EX_VDC_RST (Tied to groun in the module, holds the video chip in the Coleco reset)

 

Pins 41 and 42 on the expansion connector connect to the Phase 2 clock and R/W lines inside the expansion module. These pins don't aren't connected to anything inside the Colecovision. The only thing I can think is that these where used as test points during development.

 

So to make the expansion module stand alone you would need to supply +5, +12 and -5 , and the clock to the unit, tied the reset to ground or a reset switch, and connect the video and audio outputs to an RF modulator.

 

 

Dan

[Paul Slocum]

So to make the expansion module stand alone you would need to supply +5, +12 and -5 , and the clock to the unit, tied the reset to ground or a reset switch, and connect the video and audio outputs to an RF modulator.

 

Do you think it would be possible to get rid of the +12 and -5 requrements? I don't think any of the 2600 logic chips need those.

 

And do you know what it would take to generate the clock signal? Is it as simple as a crystal and a chip? I'm not much of a hardware person.

-Paul

[DanBoris]

Do you think it would be possible to get rid of the +12 and -5 requrements?  I don't think any of the 2600 logic chips need those.

 

I was thinking about this also. The voltages to enter the circuits in the expansion module so they are being used for something. I'll need to trace the circuit to see how there are used.

 

And do you know what it would take to generate the clock signal?  Is it as simple as a crystal and a chip?  I'm not much of a hardware person.

-Paul

 

Not exactly sure what you would need, but it would probably be a pretty simple circuit.

 

Dan

[Curt Vendel]

Wouldn't it be easier to just monkey around with the Coleco Gemini?

 

 

 

Curt

[a2dconverter]

I don't know why I did it... I had a second expansion module #1 that I decided to make standalone with the info from this topic...

 

Here's some pix...

 

 

 

 

Standalone EXM1.pdf

 

 

Seeya

 

Joe

Edited October 28, 2020 by a2dconverter

[Falonn]

On 2/8/2003 at 4:59 PM, Paul Slocum said:

Do you think it would be possible to get rid of the +12 and -5 requrements? I don't think any of the 2600 logic chips need those.

I'm also curious about this ~21 year old question.  Poking around in @ChildOfCv's excellent schematics (and comparing/contrasting with the original 2600 using some 2600A Rev 16 schematics I found on the RetroSix wiki; the last image on that page), it looks like both the +12V and -5V lines from the Colecovision expansion port are being used for something.

 

12V

The +12V line is pretty straightforward.  It looks like the color adjust pin on the TIA has an input range just a little wider than 5V.  Here is a side-by-side comparison of that part of each, simulated in Falstad.

 

 

The +9V on the 2600 side is from the unregulated power supply input.  The +5V in both come from a 7805-like regulator (even though Expansion #1 already has a regulated 5V supply coming in, it still includes another regulator from 12V to 5V).

 

So the trim pot will swing from 0V to 5.9V (instead of maxing out at 5V if they'd just used the 5V supply directly).  Without adding a small boost converter someplace, this one looks like it's actually required.

 

-5V

This one is a little weirder.  There's nothing analogous to it in the original 2600, so there isn't anything to compare it to.  The only place it looks like it's being used in Expansion module #1 is for the controller ports:

 

 

The 1N5222B's there are 2.5V Zener diodes.  And pin 8 of the controller ports are supposed to be GND.  Simulating this in Falstad, instead of getting 0V on both pin 8's, they're seeing something like -60mV, with 18ohms of impedance to ground, which seems strange to me.

 

Worse, between ZD1 and R1, this circuit is always burning ~200mW for nothing.

 

If you just disconnect the -5V supply, you save those 200mW and the ground pins on the controllers actually see 0V (granted, it's through R33 which isn't great).

 

Am I missing a reason why you'd want the controller GNDs to be slightly negative?  I know the hardware designers back then were analog wizards, so I just assume everything is more clever than it seems, but seeing a redundant 5V regulator makes me wonder a little.

[ChildOfCv]

I suspect that the zeners were added because the Coleco controllers may have had different trigger points than the Atari controllers.  They're supposed to be somewhat compatible, at least pinout-wise.  But maybe these were added to fix potential problems that were caused by the CV controller's diode maze.

 

Come to think of it, I wonder if the number pad on the CV controller has any compatibility with Atari's keypad controller?

 

That said, I still don't understand ZD1's existence, not even in that context.  Maybe it's an anti-static measure from plugging the module in.

[ChildOfCv]

On 2/8/2003 at 2:59 PM, Paul Slocum said:

Do you think it would be possible to get rid of the +12 and -5 requrements? I don't think any of the 2600 logic chips need those.

The difficult part there is that the final video output amplifier on the EM1 uses +12V.  While 5V would provide plenty of room for a video output signal, the amplifier is optimized for +12V, and may need some parts replaced if you wanted to run it on +5V instead (and then it would no longer be compatible with the CV).

 

The -5V may be optional, but it's hard to know without removing it and testing.

 

As for generating a clock signal, there are some blank spots on the board where a NAND gate chip, a crystal, and some resistors and capacitors could be soldered in.  Theoretically, this is an onboard clock circuit.  There is a jumper that connects the expansion port's clock into the system, but it can be moved to the jumper spot at the output of this circuit.  Or you can just forget about all that and do the full replacement like another poster did.