Rice Lake Okidata 320-390-420 Turbo - Service Guide - Manual (Page 141)

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Service Guide ML320/321Turbo
Chapter C Software Diagnostics and Adjustments
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.
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