Radio Shack TRS-80 PT-210 Service Manual page 33

Photo Interrupt
The photo interrupt determines the print start position.
a
During carriage return, it detects an
signal, sends a signal to the pCPU, and causes the carriage return
motor to stop.
Light emitting element
Light emitting
Light receiving element
(Photo Transistor)
11
I/O Port
P60
8243
Figure 24.
unit
Figure 25.