Maple Systems OIT Family (ASCII) - Manual (Page 60)

RS-485 Network Cabling
IMPORTANT! The OIT3200B, OIT3250B, OIT3600B, OIT4400B, OIT4450B, and
OIT5400 have a jumper that must be moved to Position B when using RS-485 communica-
tions in a network. Refer to the “Set Jumper for Specific Protocol” section in the Installation
Manual.
If multiple OIT’s are to be connected to an ASCII host, then each OIT must be configured to
operate in Network mode. Network mode allows an ASCII host (located at one of the net-
work ends) to communicate to multiple OIT’s via a single, continuous 5-wire data link. Al-
though a maximum of 100 OIT’s can be connected to a network, the actual number depends
upon the transceiver loading, data rate, and cable capacitance of the network. Therefore, the
actual number may be less. Network repeaters can be added to boost the RS-485 signal and
extend the number of OIT’s that may be connected.
The 5-wire network data link consists of 2 sets of twisted pairs and a signal ground. One of
the twisted pair is connected from the ASCII host’s transmit lines to all of the OIT’s receive
lines. The other twisted pair has all of the OIT’s transmit lines connected together and going
into the ASCII host’s receive lines. The single wire is used as a communications signal
ground.
The network data link must be properly terminated to reduce the amount of interference and
noise pickup from the surrounding environment. This is accomplished by using terminating
resistors at both ends of the network cable. Figure 6 shows a typical termination circuit. The
ASCII host termination shown is only needed if the ASCII host’s RS-485 port does not con-
tain any built-in terminator circuitry. The end termination must be done at the extreme end of
the network cable. If the network cable ends at the last installed OIT, the end termination can
be connected using that OIT’s connecting cable.
CABLING 59
1010-0088, REV02
HOST CONTROLLER
TxD+
OIT3160A/OIT3200B
OIT3250B/OIT4160A
OIT4400B/OIT4450B
PORT 1 OIT3600B
TxD-
RxD+
RxD+
RxD-
TxD+ 4
1
9
PIN
4
5
6
PIN
RxD- TxD-
SIG GND SIG GND
6 7
5 8
Figure 5 RS-485 Pinouts