USER'S GUIDE
ADVANCED PACKET OPERATION
PK232UG Rev. B 9/86
5-3
94
Some computers have difficulty simultaneously sending and receiving characters over the
serial port. This is most commonly the case for computers with "software UARTs". Type-in
flow control improves the operation of such computers with your PK-232.
5.3.2.
Data Flow Control
In Command Mode, your PK-232's input buffer may fill up if you try to type a command
that is too long. In Converse Mode the buffer may fill up for any of several reasons: you
may be using a faster serial port baud rate than the radio data rate, radio data transmis-
sion may have slowed down because of noise or other users on the channel; the other
person or computer may have stopped output from that system.
Your PK-232 signals the computer to stop sending data when there is a room remaining
for about 80 characters in the buffer. When the buffer fills up entirely, data will be lost.
When the buffer empties to the point where there is room for at least 270 characters,
your PK-232 signals the computer to start sending data again.
A computer file transfer program may be unable to process data fast enough to keep up
with output from your PK-232. A computer must respond to interrupts from its I/O devices
in order to read every character. Some simple programs may poll the input register for
new data. Data may be lost if the polling is not done often enough. Some computers dis-
able interrupts during disk accesses. If the program enters a routine which doesn't allow it
to check for data or respond to it, the computer should signal your PK-232 to stop send-
ing data.
Your PK-232 provides two methods of flow control:
o
XON/XOFF flow control, sometimes called "software flow control", sends a special
character (usually <CTRL-S>) to stop the output and another special character
(usually <CTRL-Q> to restart the output.
o
Hardware flow control requires that both computers use the CTS (Clear To Send)
and RTS (Request To Send) lines of the RS-232C standard.
Some commonly used file transfer and terminal programs for home computers do not pro-
vide flow control in software; many serial ports do not support hardware flow control.
Although the RTS and CTS lines appear at the connector, they may not to be used on
some computers unless the software reads the state of the CTS line. If your PK-232
seems to lose data during file transfers, flow control is probably the problem.
5.3.2.1.
XON/XOFF (Software) Flow Control
Set
XFLOW ON
to use XON/XOFF flow control if your terminal program doesn't provide
CTS/RTS (hardware) flow control.
The special flow control characters are set to <CTRL-S> and <CTRL-Q> by default, but
can be changed.
o
The
XON
and
XOFF
commands define the characters sent to the computer by your
PK-232.
o
The
START
and
STOP
commands define the characters sent to your PK-232 by the
computer.
After sending a
STOP
character, your computer may receive as many as four characters
from your PK-232; some characters may already be "en route" through serial I/O chips.
