GTCO Cordless Roll-Up - Users Guide - Manual (Page 37)

Cordless Roll-Up 37
Flow Control
Flow control is the process of regulating the traffic or flow of data between two RS-232C
devices. Flow control prevents the transmission and subsequent loss of data if the receiver
is not ready to accept it. Examples of devices that use flow control are: a printer to signal
buffer full; a modem to indicate carrier detect; and a time-shared computer that services
multiple users on a time-available basis.
There are two kinds of flow control:
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Software flow control is often used over communication links where only a 3-wire cable
is used (Transmit Data, Receive Data, Ground) or over telephone lines. The Cordless Roll-
Up is equipped for software flow control. It will immediately stop sending data when it
receives an ASCII XOFF character (CTRL-S, hex 13). Transmission will resume when it
receives an ASCII XON character (CTRL-Q, hex 11). Character flow control will work with the
straight through cable and the null modem cable.
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Hardware flow control (also called modem lead flow control) uses one or more lines in
the RS-232C cable to send status signals from one device to another. The Cordless Roll-Up
is not equipped for hardware flow control.
Remote Commands
NOTE: The following information is not required for normal Cordless Roll-Up operation.
Cordless Roll-Up can receive commands from other devices through its RS-232C port.
Commands cause the Cordless Roll-Up to change the way it operates, to use certain
coordinate formats and to do other things directed by you or by an application program.
Commands offer another way to control Cordless Roll-Up operation besides the Custom
Configuration Menu. Certain Cordless Roll-Up functions can be carried out only through
commands.
If you are developing your own application software, be cautious about using commands in
your program. An interruption in power to the Cordless Roll-Up or a Reset will cause it to
discard any command changes it has received. This could leave the program confused
about what the Cordless Roll-Up is doing. A full system reset would then be needed to get
the digitizer and computer coordinated again.