Moxa Technologies CP-118U user manual Addc

CP-118U User’s Manual Serial Programming Tools

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.

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