•
SIGNAL
TIME
FUNCTION
IN/OUT
PIN
Handshake output, high
out
1
AUXOUT-
Handshake output, low
out
6
T X D +
Transmit data, high
out
2
TXD-
Transmit data, low
out
7
GND
Ground
--
3
RXD-
Receive data, low
in
8
RXD+
Receive data, high
in
4
AUXIN-
Handshake input, low
in
9
AUXIN+
Handshake input, high
in
5
Not used
--
--
•
•
956 Manual
August 1994
RS-485 Usage -
J2 Full Duplex
Table 3-14 lists the connector pin assignments for the serial port COMB J2. I t is configured as full
duplex RS-485 port, in accordance with Tables 3-3 and 3-11.
Table 3-14. C O M B Pin Assignments Full Duplex (RS-485)
The signal lines shown in Table 3-14, provide for a full duplex operation with handshaking. RS-485 is
a differential interface, which provides for greater immunity against noise and interference. This
interface will drive cable lengths up to 4000 feet at 57.6K bps. Terminators (120 ohms) are provided
for the RS-485 input signals RXD and AUXIN. These terminators are installed by shorting W16 and
W17 (refer to Tables 3-11 and 3-12).
The handshake signals usually present on an RS-232C interface (RI, DSR, DCD, CTS, RTS, and DTR)
are not fully supported on the RS-485 interface. Instead, RS-485 uses AUXIN and AUXOUT. F o r
maximum software compatibility, the RS-232C Clear to Send (CTS) handshake input signal for the
serial controller is derived from the RS-485 AUXIN signal. Similarly, the RS-485 AUXOUT signal is
derived from the RS-232C Request to Send (RTS) handshake output signal from the serial controller.
The remaining handshake input signals (RI, DSR, and DCD) are tied active by the jumpers installed at
W11, W13, and W14 when this port is configured for RS-485, (refer to Tables 3-11 and 3-12).
If the RS-485 device which you are connecting to this port does not provide an AUXIN signal, then
(depending on the software you are running) you may need to loop AUXIN to AUXOUT.
Alternatively, you can short W12 pins 1/2 instead or 2/3 to force CTS active.
3-11
