The Tandy TRS-80 Colour Computer (CoCo 1, 2, and 3) provides a 5-pin DIN cassette port for storing and loading programmes on standard audio cassette tape. Specified as “5P DIN 1500 baud” in Tandy service documentation, the interface uses frequency-shift keying (FSK): 1200 Hz represents a binary 0 and 2400 Hz represents a binary 1, yielding approximately 1500 baud. Two pins carry motor relay control, allowing the computer to start and stop the cassette transport under software control via the PIA (Peripheral Interface Adapter); read and write operations pass through a zero-crossing detector and a 6-bit DAC respectively, with the audio signal attenuated to approximately 1 V peak-to-peak into a 2 kΩ load.
| Pin | Description |
|---|---|
| 1 | Motor Relay |
| 2 | Ground |
| 3 | Motor Relay |
| 4 | Signal Input |
| 5 | Signal Output |
Signals
- Motor Relay (pins 1 and 3) — both pins drive the cassette motor relay; motor is switched on (bit 3 of PIA address FF21 = 1) or off (= 0) under software control, keeping the tape moving only during actual data transfer.
- Ground (pin 2) — signal and chassis ground reference.
- Signal Input (pin 4) — audio data received from the cassette EAR/playback output; a zero-crossing detector in the SALT chip reads the FSK signal at PIA address FF20 bit 0.
- Signal Output (pin 5) — audio data sent to the cassette MIC/record input; the CoCo 1 and 2 output is derived from an attenuated DAC at approximately 1 V p-p into 2 kΩ; the CoCo 3 uses a 6-bit DAC coupled through the same SALT chip.
Notes
- Connector type: 5-pin DIN (180° layout), female socket on the computer.
- The interface is compatible with any standard audio cassette recorder that provides a MIC input, an EAR output, and a remote motor control socket.
- Pins 1 and 3 together form the motor relay circuit; they connect to the cassette recorder’s remote jack to switch the motor on and off.
- Data encoding is sinewave FSK: one cycle of 1200 Hz encodes a 0 bit; one cycle of 2400 Hz encodes a 1 bit.
- The CoCo 3 cassette relay is driven by the SALT chip (IC8 pin 9); motor control is via PIA IC4.
References
- TRS-80 Color Computer Technical Reference Manual — Radio Shack / Tandy Corporation, 1981 (Cat. 26-3193)
- Tandy Color Computer 3 Service Manual — Radio Shack / Tandy Corporation (Cat. 26-3334)