Saturday, October 6, 2012

The Apple 1 Cassette Interface


The Apple Cassette Interface (ACI) was the only accessory sold for the Apple 1 computer. It allowed saving and loading programs from cassette tape using an inexpensive tape recorder.

Vince Briel  recently made a batch of replica ACI boards both as kits or pre-assembled. The board is similar to the original except using a more easily obtainable EEPROM chip rather than the ROM chips on the original design. I got one of the first batch of kits and assembled it.

ACI parts and manual ready to be assembled
I have a couple of tape recorders from that era. I have a GE model that I bought around 1980 and used with my Ohio Scientific Superboard computer for tape storage. I also recently picked up a Panasonic model from the 1970s or 1980s at a thrift store.  I don't the Panasonic RQ-2102 model that Apple originally recommended (amazingly it is still be manufactured and available).

GE Cassette Recorder circa 1980
Panasonic Recorder picked up a thrift shop
Panasonic RQ-2102 Recommended by Apple
The original Apple Cassette Interface manual is available on-line. The software is on-board the ACI and consists of only 256 bytes of code written by Woz. It is primitive and has no error detection. The later Apple II had a similar cassette interface circuit built into the motherboard (in models up to the Apple 2c). The Apple II used a similar storage scheme but added a checksum verification to detect errors.

Assembled ACI Replica
I haven't got mine to work reliably yet. I am working with some other kit builders to track down why. It is known to be tricky to get working. As well as a tape recorder I've been using my computer's sound card and an oscilloscope to debug it. I'll report more here on my progress toward getting it to work reliably. 

ACI Installed in the Replica 1

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