Operational Description Of The Control Unit - Radio Shack TRS-80 PT-210 Service Manual

Operational Description of the Control Unit
Symbols used in the description of control logic are listed in the following table:
Symbol Description
Key matrix output signals
Key matrix input signals
SHIFT
Shift input character select signal
CNTL Control key: special codes may be used
1 1 0 BPS/300 BPS select signal
Half/Full-duplex select signal
SPEED
DUPLEX
MODE
NUMERIC
REPEAT
CARRIER LEAD
ERROR LED
POWER LED
+5V (VCC)
On/Off-line select signal
Numeric; 10-key mode select signal
Repeat signal
Carrier indicating LED
Error indicating LED
Power indicating LED
+
5V power supply for logic
+
12V power supply for logic
-
12V power supply for logic
+8V power supply for motor
4-
5.0
-
6.1 V power supply for thermal head
GND
Signal ground
MGND
Magnet ground
Frame ground
Transmitter data
Receive data
Data set ready
TxD
RxD
-
DSR
-
INH Inhibit
Modem/RS232C receive data select switch sianal
SD
RD
-
DTR
-
X1
I -
X4
Send data
Receive data
Data terminal ready
Drive signals to transistors of the X-motor