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RS232 Port
The PSI BOX sets DTR out low when it is ready to
receive data. When the PSI BOX input buffer starts to fill up,
less than 128 bytes left (or only 1 if no buffer), it will set DTR
out false, this will be detected by the CTS input of the other
device. If it continues to receive data it will hold DTR out false,
the data received may be lost if there is no room in the PSI
BOX buffer. Any data received when DTR or RTS are high
high may be LOST, even if the RS232 RCVR LED flashes!
When there is more than 128 bytes of room in the PSI BOX
buffer, the PSI BOX will set DTR out true. It will remain true
provided their is still, at least, 128 bytes of space available in its
internal buffer.
_________________________ _
The XON/ XOFF Handshake.
The XON/ XOFF handshake works in the following
manner. The output lines DTR and RTS are sent out low, and
the PSI BOX does not care what state the CTS, DSR and DCD
inputs are.
It is recommended that if you are using the XON/ XOFF
handshake that the CTS, DSR and DCD inputs to the PSI BOX
are forced true.
The flow of data is governed by the sending and receipt of
the XON XOFF codes. The XON code is chr$(17), the XOFF
code is chr$(19).
When ever the PSI BOX receives XOFF, it will
immediately stop sending data until after it has received an XON
code.
The PSI BOX sends the XOFF code when it is about to
run out of room in which to store incoming data. The minimum
amount left before the transmission of the XOFF code depends
on whether the 32K buffer is enabled or not.
_______________________ _
XON XOFF Buffer In Use.
When the PSI BOX input buffer starts to fill up, less than
128 bytes left, it will send an XOFF code to the other device. If
Chapter 5
PSI BOX Reference
Page 41
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