42089201TH Rev.4 115 /
Oki Data CONFIDENTIAL
APPENDIX B RS-232C SERIAL INTERFACE BOARD (OPTION)
1. GENERAL
This section describes the operation of the RS-232C Serial Interface board installed in the Printer
as an option using a start-stop synchronization and serial communications circuit. This serial
interface board is capable of transmitting and receiving simultaneously at speeds up to 19,200
bits per second. Two protocols are available: printer Ready/Busy and X-ON/X-OFF modes.
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.
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