Expansion Connector Pin Assignment
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15-pin expansion connector has the following pin assignment:
Output signals that are present both on the DB9M and expansion connectors (DTR, RTS, TX) need not be switched. So, for example, the TX (output) line from the EM120/EM200 is connected to the RS232 transceiver IC and to the expansion connector. For input signals (RX, CTS, DSR) there must be a way to disconnect the RS232 transceiver IC from the EM120/EM200. Three jumpers (combined with pins RX, CTS, DSR of the expansion connector) serve this purpose.
For example, when the RX jumper is closed the RX pin of the EM120/EM200 receives a signal from the RS232 transceiver. When the jumper is opened you can use the RX pin on the expansion connector to supply a TTL RX signal from your own external board. Figure below illustrates this.
Maximum load for all CMOS-type lines (P0, P1, ... RX, TX...) is 10mA.