"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 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 3, 4 and 5.
B19 and B20 are not allocated on any other boards however B21 carries a 1MHz clock on the 6502A CPU Boards so I have opted for using B19, B20 and B23 as follows:
You also need to wire O2 on A29 to IC1 pin 1.
Of course you then need to make the same connections on the CPU Board:
I haven't modified a 6502A CPU Board as they are unlikely to be used with a cassette interface, in any case I don't think the cassette routines in COS would work as the 6502A uses a 6522 PIA rather than an 8154.
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: