Super Systems 20PQ - Manual (Page 20)

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3) The EIA standard establishes that by RS-485 interface it is
possible to connect up to 30 devices with one remote master
unit.
The serial interface of these instruments is based on “High
input impedance” transceivers; this solution allows you to
connect up to 127 devices (based on the same transceiver
type) with one remote master unit.
21
20
COMMON
22
B'/B B/B'
A/A' A'/A
M
A
S
T
E
R
I
N
S
T
R
U
M
E
N
T
F) SERIAL INTERFACE
Fig. 17 - RS-485 WIRING
The cable length must not exceed 1.5 km at 9600 BAUD.
NOTES:
1) This is an isolated RS-485 serial interface.
2) The following report describes the signal sense of the voltage
appearing across the interconnection cable as defined by
EIA for RS-485.
a) The ” A ” terminal of the generator shall be negative with
respect to the ” B ” terminal for a binary 1 (MARK or OFF) state.
b) The ” A ” terminal of the generator shall be positive with
respect to the ” B ” terminal for a binary 0 (SPACE or ON).
XKP-1-C2.p65 10/30/01, 9:36 AM 16