Allen-Bradley Plc-2 - Quartech 2800 Manual

2800 & 2900 Series PLC Drivers
The network described on the previous page was set up for best performance. Sometimes it is desirable to leave gaps
between devices addresses so that other devices can be easily added after the data link has been initialized. This is
acceptable, however, it will result in a reduction of performance since some device will have to issue a solicit
successor message to each unused address in the gap. If a gap is left it should be as small as possible to reduce the
link initialization time. A gap of even one address will reduce network performance.
Transmission Lines
The DH485 Data Link network is designed to be wired in a point-to-point fashion. All devices are wired in-line, one after
another, forming a single trunk line. Drop lines off the main trunk line are not recommended and may degrade or
prevent network operation. As the trunk line length increases two factors become increasingly important. These factors
are line resistance and line capacitance. In most applications the use of line terminating resistors will improve or allow
satisfactory performance. Two terminating resistors are required for a network regardless of the number of devices
in the network. One terminating resister is connected at each end of the network. The OIT includes a terminating
resistor that is switched into to the circuit by closing a DIP switch accessible through the cover. Refer to the Hardware
Manual for the particular OIT to identify which DIP switch is assigned. If the OIT is at either end of the network the
switch should be closed. Devices which are not at either physical end of the network must not have termination resistor
switched into the circuit.

Allen-Bradley PLC-2

The PLC-2 interface is intended for point to point communications, i.e., only a single peripheral device may be
connected to the PLC-2 port. However, Quartech does manufacture a port expander (Model 8516) that will allow up
to four devices to talk to a single PLC-2 processor.
ScreenMaker 2000 Port setup:
The following schematic shows the cable connections required between the OIT and the PLC-2 port. This cable is
available from Quartech in a standard length of ten feet. Cables up to fifty feet in length may be ordered.
15 Pin Male D-Type
RXDB
RXDA
CTSB
CTSA
TXDB
TXDA
Baud rate: 9600 bps
Byte format: 8 data bits, 1 stop bit, Even parity
A single Dialogue File address is assigned. This is the address of the
Command Word. The two contiguous word addresses following are also
required. The last digit of the address can not be a six of seven.
> Specified Word Address is the Command Word.
> Specified Word Address plus one is Screen Trigger one.
> Specified Word Address plus two is Screen Trigger two.
Allen-Bradley PLC-2
Quartech Part Number: 2157-10
PLC-2
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1 <
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2 <
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3 >
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4 <
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5 <
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6 <
2800/2900
15 Pin Female D-Type
< 14 TXDB
< 6 TXDA
< 15 RTSB
< 11 RTSA
< 12 RXDB
< 13 RXDA
+))))) +)))))
< 4 RTS
.))))) .)))))
< 5 CTS
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DM2829_PLC Revision 2