Control Data Corporation INFORMATION SYSTEMS TERMINAL II Hardware Maintenance Manual page 27

The transmitter idles in the mark state.
Both the receive and send portions must operate with the
same format (number of data bits, parity) and baud rates.
PLATO COMMUNICATION INTERFACE
This PLATO network-compatible communication interface
allows asynchronous reception of 2l-bit words at a nominal
1200 bps, and asynchronous transmission of l2-bit words at
a nominal 75, 120, or 1200 bps (switch selectable) via
RS-232-C or optically-coupled long line interface circuits.
This long line receiver is basically a light-emitting
diode/phototransistor circuit. The sending device should
provide enough current to drive the LED to the on state to
transmit a logical 1, and turn the current off to transmit
a logical
O.
Figure 1-3 shows the typical long line
receiver circuit.
The long line receiver data is ORed with the RS-232-C data.
An internal switch determines which of the two signal
inputs is to be used 'by the terminal.
+12
v
+5
v
LONG
LlNE+~I>_-~~--+--,
IK
DATA
LONG LI NE -
---+,>_-----4t----+~
QI
lOOK
RCVR
=
MCT2F, CDC PART NUMBER 95791300
01
=
TRANSISTOR NPN, CDC PART NUMBER 51003059
01
=
DIODE IN4148, CDC PART NUMBER 51007385
03339
Figure 1-3. Long Line Receiver
82100083
B
1-7
I
I