Oki Pacemark 4410 Service Handbook page 181

2. OPERATION DESCRIPTION
2.1 Element Description
(1) 80C51 with MASK ROM
An eight-bit microprocessor controller that controls the following:
(a.)Serial interface protocol and data transfer through a serial port.
(b.)Message buffer.
(c.)Transmission of parallel data to the printer.
(2) SN75189
An RS-232C standard line receiver
(3) SN75188
An RS-232C standard line driver.
(4) 2764
An 8 kbyte ROM that contains the serial interface control program.
(5) HM6264
An 8192-byte static RAM used as a message buffer.
2.2 Circuit Description
A block diagram is shown in Figure B-2-1.
40496501TH Draft Version
B-2