The Model I Printer Interface Cable

written by Matthew Reed

One of the limitations of the cassette-based TRS-80 Model I was that it had no printer port. There were many cassette programs designed to use a printer, such as Electric Pencil and Scripsit, but no simple way to add one. Only a few Radio Shack printers were designed to connect to a cassette-based Model I directly.

The usual approach to adding a printer was to buy a Radio Shack Expansion Interface. In addition to providing extra memory and a floppy disk controller, the Expansion Interface also added a printer port. But a fully equipped Expansion Interface cost more than a Model I itself, and a unit with no memory still cost $299.00. Another option was a lighter-weight third-party Expansion Interface, such as the Microtek MT-32 or Exatron MM+. But this was still overkill if all you wanted was a printer.

The Printer Interface Cable, introduced by Radio Shack in 1979, was a special cable that allowed a cassette-based Model I to be connected directly to a printer. Each Printer Interface Cable was six feet long and attached between a printer and the bus connector of the Model I. No Expansion Interface was required (and in fact, it wouldn’t work with one).

There were two versions of the Printer Interface Cable. They differed only in the printer connector used:

• Printer Interface Cable (catalog number 26-1411), also known as the Quick Printer Interface cable, was for printers that used a Centronics connector (which was most of them). At the time it was introduced, this included the Quick Printer (but not the Quick Printer II) and the Line Printer I.
• Line Printer II Interface Cable (catalog number 26-1416) was for the few Radio Shack printers that used a card edge connector rather than a Centronics connector. Radio Shack once identified those printers as the Line Printer II, Line Printer IV, Quick Printer I, and Screen Printer.

Each cable originally cost $79.00 when introduced in 1979. Those prices were reduced to $59.00 just a few months later.

In comparison, the equivalent printer cables which connected directly to the Expansion interface were less expensive:

• The Model I printer cable with a Centronics connector (catalog number 26-1401) cost $39.00.
• The Model I printer cable with card edge connector (catalog number 26-1415) cost $29.00.

The Model I was followed by the Model III in 1980 and Model 4 in 1983. Both of those computers included a printer port in all their configurations, even the cassette version.