HP 24SII - Manual (Page 66)

The Model 24SII Data Exchange System allows pairs of computers
(or computers and other devices such as modems, scales, data
collection equipment, etc.) to communicate while other computers are
sending data to the print buffer and the Model 24SII DES is sending
data to printers. Full duplex communication allows file transfer with
many popular communications software packages.
NOTE: Computer-to-computer communication can occur only if both
ports communicating are serial. Parallel ports allow one-way
communication only and will not provide full duplex communication.
Computers that will be operating with computer-to-computer
communication must both be connected to ports designated as serial
ports. For high speed serial modules, the printer sharing mode must
be bidirectional.
If two serial computers wish to communicate, either computer sends
to the Model 24SII DES the Port Select Code followed by the other
computer's module number and port number, and a terminating
character: 0D Hex (Enter/Return) or 0A Hex (Line Feed).
If the requested computer is free, the two computers are connected
with full duplex communication, and an
On Line message is sent by
the Model 24SII DES to the computer requesting the connection.
If the requested computer is busy, the computer requesting
connection receives a
Busy message from the Model 24SII DES.
To disconnect, either connected computer first delays two seconds
and then sends the Port Select Code followed by a terminating
character: 0D Hex (Enter/Return) or 0A Hex (Line Feed). You must
wait another two seconds after sending the disconnect sequence,
before sending any other data such as a print job or Port Select Code.