6.2.10.3 Operating Notes
For reference, see the tables under Serial Port Pin Assignments in Section 5:.
Support for the DTR output signal is provided for COM1 only, on all RX3i models (except
CPE302, CPE305, CPE330, CPE400 and CPL410), in Rel 7.16 and later releases.
For CPU COM2 (RS-485), the RTS signal is also controlled by the transmit driver.
Therefore, control of RTS is dependent on the current state of the transmit driver. If the
transmit driver is not enabled, asserting RTS with the Write Port Control COMMREQ will
not cause RTS to be asserted on the serial line. The state of the transmit driver is
controlled by the protocol and is dependent on the current Duplex Mode of the port. For
2-wire and 4-wire Duplex Mode, the transmit driver is only enabled during transmitting.
Therefore, RTS on the serial line will only be seen active on COM2 (configured for 2-wire
or 4-wire Duplex Mode) when data is being transmitted. For point-to-point Duplex Mode,
the transmit driver is always enabled. Therefore, in point-to-point Duplex Mode, RTS on
the serial line will always reflect what is chosen with the Write Port Control COMMREQ.
6.2.11 Cancel COMMREQ Function (4399)
This function cancels the current operations in progress. It can be used to cancel both
read operations and write operations.
If a read operation is in progress and there are unprocessed characters in the input buffer,
those characters are left in the input buffer and available for future reads. The serial port is
not reset.
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