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The Color Computer has an expansion port. What is the pin out? What are the kinds of devices that can be used with it? How was the Multi-Pak involved?

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There are two variations of the cartridge port on the Color Computer lines. The attached image shows the pin out of the CoCo 2 & 3.

CoCo 2/3 cartridge port

The CoCo 1 cartridge port is slightly different, in that it offers -12 volts DC on pin 1 and +12 volts DC on pin 2 (from the Color Computer Technical Reference Manual (Tandy).pdf file available here):

CoCo 1 cartridge port

The CoCo 2 & 3 do not produce 12 volts DC. Due to this, several devices listed below, i.e.: X-Pad, cannot be used on a CoCo 2 or 3 without a Multipak Interface, which does produce the 12 volts DC required.

The Multipak Interface (MPI) was a device used for bus expansion on the Color Computers. It offered four slots for cartridge devices; either hardware or software selectable. Tandy made three basic models of the MPI, while other manufactures made their own versions as well. Below is a partial list:

  • A-Bus (Alpha Products)
  • BT-1000/2000 (Basic Technology)
  • CC-Bus (PBJ Inc)
  • CX-P1 Color Computer Expansion Interface (General Automation) cocoman3
  • Slotpak III (Chris Hawks/Howard Medical)
  • XPort (Orion Technologies)
  • Computize Y-Box
  • Spectrum Switcher
  • Owl-Ware Super I/O
  • Tandy Multipak (26-3024)
  • Tandy Multipak (26-3124)
  • Tandy Multipak (26-3214A)

(Only the 26-3124A was ready to be used with a CoCo 3 due to the change in the CoCo 3's addressing. The other two models had to have a fairly simple mod done)

  • The Solution (Frank Hogg Labs)
  • USER-80C (J-NOR Industries)
  • Y-Cable
  • XPANDR1 CoCo Expander Card (Robotic Microsystems)
  • XPANDR2 CoCo Expander Card (Robotic Microsystems)

Other type of devices are able to be used as well - MIDI devices; graphics tablets such as Radio Shack X-Pad; numerous types of disk storage, both floppy and hard.

For a mostly complete list of the devices and pictures of most of them, as well as other hardware devices for the Color Computer lines, this link provides much more information.

  • Interesting... the Atari's lost 12V in their serial ports when they were revved to. I assume for the same reason - by that time it was a lot cheaper to build a modem that ran at 5V than have a PSW with 12V and two RS232 encoders. Its one thing when Hayes was the only game in town, it's another when Rockwell 300bps drivers were $5CAD at Electrosonic in Toronto. – Maury Markowitz Oct 12 '18 at 17:48
  • I can confirm the 26-3124A does work with the COCO3, I have one. When the PEEK command "PRINT PEEK(&HFF90)" is ran it returns a value of 126. If you get 255 then your MP needs the PAL upgrade. – dalhend Jan 7 at 15:30
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The UK-based Dragon 32 was a close cousin of the Color Computer, and used the same pinout as the CoCo 1 on its expansion socket. A small number of games were released in cartridge format for the Dragon. The original manufacturer, Dragon Data, made a floppy disk interface, EPROM programmer, and modem interface for the expansion socket. Third-party manufacturers also produced a selection of expansions. Descriptions and photos of many of these (and other accessories) can be seen on the World of Dragon website.

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