Kantronics MT1200, User Manual

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Which way you implement this depends on the capabilities of your computer
communications program and personal preference. The cable between your computer
and TNC must also be wired appropriately.
Software Flow Control
Software flow control sends special characters on the TXD and RXD lines of the RS232
cable. These are the same lines used for sending regular data between the TNC and
computer. Software flow control normally sends a <Ctrl+S> to stop data and a <Ctrl+Q>
to restart data. When a buffer gets close to full, the device will send a <Ctrl+S> and
expect the other device to stop. When the buffer gets nearly empty, it will send a
<Ctrl+Q> to tell the other device to send more data. How full or empty a buffer is, when
the special characters are sent, is determined by the program. But, since the regular
data lines are being used, a <Ctrl+S> sent as data from the keyboard will also stop data
from the TNC. And likewise, if there is a <Ctrl+S> in a file being sent, data flow from the
TNC will stop until a <Ctrl+Q> is received.
XFLOW needs to be turned ON for the TNC to use software flow control. XOFF
determines the character sent by the TNC to stop the flow of data from the computer,
and the XON character restarts the flow. The TNC expects the computer to send the
STOP character to stop data to the computer and the START character to restart data.
To use software flow control these commands would be set as follows: XFLOW ON,
XOFF $13, XON $11, STOP $13, START $11. (Default settings.)
Two commands are provided to make it possible to send and/or receive these special
characters in Transparent Mode and still use software flow control. TXFLOW enables
flow control sent by the TNC to the computer and TRFLOW enables the TNC to
recognize flow control sent by the computer. If both these commands are ON (and the
above commands are set as stated) then software flow control will take place in both
directions, to and from the TNC and computer.
If you are in Transparent Mode sending a file, the computer does not need to tell the
TNC to stop and start (since you are sending the file). By turning TRFLOW OFF and
TXFLOW ON, the TNC will accept START and STOP characters embedded in the file
and send them along to the radio as data. Meanwhile, the TNC can send the XOFF and
XON characters to the computer to control the flow of data from the computer. When
receiving a file, turn TRFLOW ON and TXFLOW OFF; the computer will accept all data
and use START and STOP characters to control the flow of data from the TNC.
Hardware Flow Control
Hardware flow control monitors the voltages on the RTS and CTS pins of the RS232
cable. Therefore these two pins must be wired between your TNC and a connected
computer. The TNC holds CTS high as long as it can receive data. Once its buffer gets
full, it pulls this line low. The computer program monitors this line. When it is pulled low,
it knows to stop sending data. When the line is again pulled high by the TNC, the
computer program will restart sending data. On the other hand the computer holds RTS
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