Oki Pacemark 4410 Service Handbook page 183

2.2.1 Operation at power on
After power is turned on, an RST OUT signal is sent from the printer control board to reset the
printer. When the reset is canceled, the 80C51 CPU performs initialization. Initialization consists
of setting the 80C51 timer, and setting the serial mode.
2.2.2. RS-232C interface
The DTR, SSD, TD and RTS signals output by the 80C51 are converted to RS-232C signals by
line driver SN75188 (Q1) and sent to the interface.
In addition, signals DSR, CTS, CD, and RD on the RS232C interface are converted to TTL level
by line receiver SN75189 (Q2) and input to the 80C51.
40496501TH Draft Version
B-4