"The upper Eurocard of the System 1 is available without
the keypad and display when it performs as a Cassette Interface card in System
2. It may also be added to Systems 3, 4 and 5 if desired. The Computer Users
Tape Standard (CUTS) frequency modulates data on to a standard audio cassette
recorder with a two tone system in which 2.4KHz represents a logic 1 and 1.2KHz
a logic 0.
If the Keyboard, Display & Cassette Interface Board is fitted in a card frame as a Cassette Interface Board then a number of signal lines need to be wired to the 64-way connector. The System 2 Technical Manual suggests using B-side pins 19, 20 and 21 for CASIN, CASOUT and NHITONE respectively whilst the 6502A CPU Board uses pins B3, B4 and B5.
There is more discussion about this on my Replica Keyboard, Display & Cassette Interface Board page.
Schematics:
Note: all 3 versions of the schematic have an error at IC2: pins 5 and 6 are transposed i.e. IC2/pin 5 should go to IC3/pin 6 and IC2/pin 6 should go to IC3/pin 8.
Documentation:
Refer to the System 1 Technical Manual
Photos:
200.001 Issue unknown [0]
200.001 Issue unknown [7]
This example was probably intended as just a Cassette Interface, perhaps for a System 2, as the display/keyboard and 7445 driver have not been fitted.
Replica Board: