GTCO AccuTab II - Users Guide User Manual
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AccuTab II 31
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:
Software flow control is often implemented over communication links where only a
3-wire cable is used (Transmit Data, Receive Data, Ground) or over telephone lines.
The sending device (such as the AccuTab) 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.
Hardware flow control is not commonly used with digitizers and is therefore not
supported by the AccuTab Controller.
Flow control may not be needed when a terminal or digitizer is directly connected to a
single-user computer. Most digitizing application software does not use flow control of
either kind.
Remote Commands
NOTE: The following information is not required for normal AccuTab II operation.
If you are programming for the AccuTab II product line, the details will be helpful.
AccuTab II can receive commands from other devices through its RS-232C port.
Commands cause the AccuTab to change the way it operates, to use certain coordinate
formats and to do other things as directed by you or by an application process.
Commands offer another way to control AccuTab II operation besides the Custom
Configuration Menu. Certain AccuTab II 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 AccuTab II or a Reset will cause it to discard
any command changes it has received. This could leave your program confused about