Moxa Technologies INTELLIO C218 - Manual (Page 69)

Serial Programming Tools
Intellio C218Turbo /PCI User's Manual 4-15
RS-485 Programming for Opt8J
If you intend to do RS-485 communication with Opt8J, please follow the RS-485
programming guide below and also refer to Chapter “Connection Option (Opt8x)
and Cable Wiring” for more Opt8J RS-485 operation details.
The Opt8J supports only 2-wire half-duplex RS-485 communication. Data+/-
pins are served for both data transmitting and receiving, depending on the RTS
signal.
The port switch of each port should be set to On position. The port is for
transmitting data if RTS is asserted and for receiving data if RTS is not asserted.
RTS scheme is suitable for any system, including Windows NT and Windows 95/98,
DOS, or UNIX, that permits RTS control from application programs.
How to transmit and receive data under Windows NT and
Windows 95/98
We recommend you to configure
Intellio C218Turbo/PCI ports as follows in order to
acquire precise timing control in RS-485 2-wire transmission.
First set the “Transmission Mode” in the configuration program to “Classical”.
UART FIFO status has no effect under the circumstance.
There are 2 solutions to control RS-485 2-wire transmission.
Solution 1
The following model is common in RS-485 2-wire transmission.
sio_SetWriteTimeouts(port, 0); /* Set sio_write() into block mode */
sio_RTS(port, 1); /* Turn on RTS signal. The RS-485
port is ready for transmitting data. */
sio_write(port, buff, 10); /* Write 10 byte characters in "buff".
The function
blocks until last
character transmitted */
sio_RTS(port, 0); /* Turn off RTS signal. The RS-485
port is ready for receiving data. */
sio_read(port, buff, 10); /* Read 10 bytes */