Watlow Series 942 Data Communications - Manual (Page 12)

12 WATLOW Series 942 How to Use Data Communications
XON/XOFF
How To Start and Stop Communicating
with the Series 942 and XON/XOFF
Starting communications with XON/XOFF Protocol is simple. You just config-
ure your computer to agree with the Series 942 communication parameters
and open its serial communication port in software. Then begin to "talk" by
transmitting a message to the Series 942. You stop communicating with XON/
XOFF Protocol simply by ceasing to send messages.
To send the message on Page 11, Figure 5, you key the ASCII characters into
your computer, or write them into your program. The computer, in turn, will
send a string similar to the one at the bottom of the example,
3D2041314C4F20353030.
Notice that we haven't mentioned protocol here, or any characters added to
this syntax by a protocol. With XON/XOFF, the message above can be
transmitted with only an additional Carriage Return <CR> (hex 0D) character
at the end. However, the ANSI X3.28 Protocol requires an envelope of Start of
Text <STX> (hex 02) and End of Text <ETX> (hex 03) characters around the
information you see above. You'll learn how to do that in the pages ahead.
XON/XOFF Protocol for RS-423A
XON/XOFF (flow control) Protocol allows a communicating device (either a
942 or the host) to suspend transmission of all messages from the other device,
and then to continue transmission when it's again ready.
The device that needs to suspend transmission sends the XOFF character
(hex 13) to stop the other device's transmitter, and XON (hex 11) to restart it.
Note that technically any character will restart the transmitter, but only the XON
character is not a part of any regular message that may be transferring.
Messages transmit according to the syntax described in the XON/XOFF formats
which follow for each command.
The XON/XOFF Protocol requires a Carriage Return character
(hex 0D) at the end of every message.