Watlow Series 988 Family - Manual (Page 15)

Data Communications with the Watlow Series 988 Family Hardware and Wiring, Chapter 2 2.3
Wiring
EIA-485 Interface Wiring
The EIA-485 communications uses a three-wire, half-duplex system. There are two
lines for transmitting and receiving and a common line. Only one device, the
computer or a controller, can be speaking at a time. The controller requires at
least a 7-millisecond delay between transmission and receipt of data. With
EIA-485 you can have from one to thirty-two controllers connected to a computer.
This diagram is a typical wiring example for units shipped after 1993 (see ç
Caution on this page). The connections on the host computer may vary, depend-
ing on the model. Refer to your computer user's manual for specific information.
NOTE:
The Electronic
Industry Association
EIA-485 standard
recommends a
maximum total
network distance of
4,000 feet.
Com
T-/R-
T+/R+
B
A
Gnd
Converter Box or Card
Controller #1
Controller #2
T+/R+ 3
As many as 32 units can be
connected to an EIA-485 network.
T-/R- 4
Com 7
T+/R+ 3
T-/R- 4
Com 7
Com
Gnd
T-/R-
A
T+/R+
B
+5V
120
Ω
1K
Ω
1K
Ω
Converter box
or card
terminals with
termination,
pull-up and
pull-down
resistors.
If the system does not work properly it
may need termination resistors at each
end of the network. A typical installa-
tion would require a 120-ohm resistor
across the transmit/receive terminals (3
and 4) of the last controller in the
network and the converter box or serial
card. Pull-up and pull-down resistors
may be needed to maintain the correct
voltage during the idle state.
Figure 2.3 -
EIA-485 Interface
Wiring Diagrams.
T+/R+ 4
Com 7
T-/R- 3
Controller
ç
CAUTION:
For older Series 986-
989 controllers with
a "date code" of
4693 or earlier,
terminal 3 is T-/R- (A)
and 4 is T+/R+ (B).
(See Diagnostics
Menu in the User's
Manual.)