VIC-1112 IEEE-488 interface cartridge

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The VIC-1112 IEEE-488 interface cartridge.
VIC-1112 with silver metal label.
Inside of the VIC-1112.

The VIC-1112 IEEE-488 interface is a device which plugs into the VIC-20's cartridge port. It allows the computer to communicate and control peripherals conforming to the IEEE-488 digital communications bus (developed by Hewlett-Packard). The cartridge has an additional male edge connector protruding out of its "back" side. It is to this connector that IEEE-488 peripherals can be attached. A curious observation is that while a "hole" or slot for such an edge connector is present on all VIC-20 cartridges produced by Commodore, only the VIC-1112 made use of it.

Like most of the "utility" cartridges that Commodore produced for the VIC-20, the VIC-1112's casing is moulded in brown plastic.

The VIC-1112 was important in that in enabled VIC-20 owners to use the wide variety of "professional" PET/CBM peripherals and other third-party IEE-488 equipment. This included floppy disk drives, hard disk drives, printers, plotters and scientific devices. PET/CBM disk drives came in dual-drive models and surpassed the storage capacity and performance of both the VIC-20's datasette & the VIC-1540 floppy drive. For instance, connecting the CBM 8250 dual floppy disk drive gave the VIC-20 access to two Megabytes of storage (an amazingly large amount in 1982). However, the high price of PET/CBM peripherals meant that relatively few home computer hobbyist owned a VIC-1112.

The following instructions are adapted from the HANDIC IEEE 488 interface, which was a very similar (if not internally identical) IEEE-488 interface distributed in Sweden by Handic. As such, these commands may not be fully compatible with the VIC-1112:

Starting procedure

1. Switch off the computer (IMPORTANT!).
2. Connect the VIC-1112 to the Cartridge port in the back of the computer.
3. Switch on the compute.
4. To start IEEE 488 ENTER: 
SYS 11*4096 <RETURN>
SYS 45056 <RETURN>

Connection of IEEE-units

In order to connect the VIC-1112 bus to IEEE peripherals, the Commodore PET
to IEEE 488 cable (part no 320101) is to be used. The Commodore-label on the
cable connection has to face upwards!

Cable length

The bus can have 15 or fewer devices connected to it at any given time. The
length of cable between devices cannot exceed 4 meters. The total transmission
length of the bus cannot exceed 2 meters times the number of connected devices,
or 20 meters (65.6 feet), whichever is less.
Schematic for the VIC-1112.

VIC-1112 ROM dump : Media:VIC-1112_ROM_DUMP.bin disassembly