HP 24SII - Manual (Page 36)

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IMPORTANT: Determine whether the devices which will connect to
the Model 24SII DES are DTE (Data Terminal Equipment) or DCE
(Data Communication Equipment). The following devices are
generally DTE: terminals, printers, computers like the IBM PC. The
following devices are DCE: modems and some computers.
If your device transmits data on Pin 2 or receives data on Pin 3, it is
DTE. If your device receives data on Pin 2 and transmits data on Pin
3, it is DCE. However, to verify the interface requirements, please
refer to the Owner's Manual for your device.
The serial ports on the M24SII-V03 I/O module has DB-25 male DTE
connectors and use the following signals for communication:
DTE PORT SIGNALS
PIN# EIA-232 DIRECTION DESCRIPTION
1 PGND ---- Protective ground
2 TX Output Data out
3 RX Input Data in
4 RTS Output + Voltage when Model 24SII DES powers-
up
5 CTS Input Model 24SII DES transmit enabled when
+12V. Internally enabled if no wire
connected.
7 SGND ---- Signal ground
20 DTR Output - Voltage when Model 24SII DES print
buffer full.