Moxa Technologies CP-118U - Manual (Page 70)

CP-118U User’s Manual Serial Programming Tools
4-6
ADDC™
ADDC™ is the best method for switching between transmission and receiving when using 2-wire
RS-485.
When using ADDC™, additional code is not required to switch between data transmitting and
receiving, since the switching mechanism is managed automatically by the board’s built-in
intelligent hardware mechanism. This means that RS-485 programming using ADDC™ mode is
just as simple and straightforward as RS-232 or RS-422 programming.
RTS
To ensure precise timing control when using 2-wire RS-485 transmission, we recommend that you
configure your CP-118U Series ports as described below.
There are 2 methods for controlling 2-wire RS-485 transmission.
Method 1
The following method is commonly used for 2-wire RS-485 transmission:
sio_SetWriteTimeouts(port, 0); /* Set sio_write() into block mode if for Windows NT and
Windows 95/98 */
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 the last character is 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 */
Method 2
The PComm or API-232 library includes a dedicated RS-485 function that integrates the functions
described in Method 1 above into one function:
sio_putb_x(port, buff, tick ); /* 1. Turn on RTS and ready for transmitting data.
2. Send data.
3. Wait for tick time.
4. Turn off RTS and ready for receiving data. */
To see more detailed information about these functions, refer to the PComm library’s on-line Help
file for Windows 95/98/NT/2000/XP/2003.