Cassette Interface - IBM 5150 Technical Reference

Cassette
Interface
The cassette interface is controlled through software. An output
from the 8253 timer controls the data to the cassette recorder
through pin 5 of the cassette DIN connector at the rear of the
system board. The cassette input data is read by an input port bit
of the 8255A-5 PPI. This data is received through pin 4 of the
cassette connector. Software algorithms are used to generate and
read cassette data. The cassette drive motor is controlled through
pins 1 and 3 of the cassette connector. The drive motor on/off
switching is controlled by an 8255A-5 PPI output-port bit (hex
61, bit 3). The 8255A-5 address and bit assignments are defined
in "I/O Address Map" earlier in this section.
A 2 by 2 Berg pin and a jumper are used on the cassette 'data out'
line. The jumper allows use of the 'data out' line as a O.075-Vdc
microphone input when placed across the M and C of the Berg
Pins. A O.68-Vdc auxiliary input to the cassette recorder is
available when the jumper is placed across the A and C of the
Berg Pins. The "System Board Component Diagram" shows the
location of the cassette Berg pins.
M
A
M A
c
c c
c
Microphone Input Auxiliary Input
(0.075 Vdc) (0.68 Vdc)
System Board 1-27