Honeywell S7800A Installation Manual page 7

MULTI-DROP RS-485 COMMUNICATION BUS. UP TO 31 S7800 SERIES 5 OR GREATER DISPLAYS CAN BE CONNECTED TO A SINGLE BUS
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WITHOUT AN RS-485 REPEATER. UP TO 99 MODBUS™ (SUBNETWORKS) CAN BE CONNECTED TO A BUS WITH RS-485 REPEATERS. WHEN
USING AN RS-485 REPEATER, THE REPEATER MUST BE INSTALLED EVERY 30TH MODULE.
THE SUBNETWORKS MUST BE WIRED IN A DAISY CHAIN CONFIGURATION. RECOMMEND THAT THE PC/PLC BE AT ONE END OF THE
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DAISY CHAIN.
MODBUS™ COMMUNICATION BUS TERMINATION RESISTORS:
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A. WITHOUT RS-485 REPEATER:
MODULES AT THE CLOSEST AND FARTHEST END OF THE DAISY CHAIN REQUIRE TERMINATION RESISTORS.
INSTALL A 120 OHM, 1/4 WATT RESISTOR BETWEEN TERMINALS A AND B OF THE PC/PLC (IF INSTALLED AT ONE END THE DAISY CHAIN).
INSTALL A 120 OHM, 1/4 WATT RESISTOR BETWEEN TERMINALS 7 AND 8 OF THE LAST S7810M MODBUS™ MODULE IN THE DAISY CHAIN.
B. WITH RS-485 REPEATER:
WHEN AN RS-485 REATER IS USED, TWO DAISY CHAIN CONFIGURATIONS ARE EFFECTIVELY FORMED. MODULES AT THE
CLOSEST AND FARTHEST ENDS OF EACH DAISY CHAIN REQUIRE TERMINATION RESISTORS. INSTALL A 120 OHM, 1/4 WATT
RESISTOR BETWEEN TERMINALS A AND B OF THE PC/PLC (IF INSTALLED AT THE END OF THE DAISY CHAIN. INSTALL A 120
OHM, 1/4 WATT RESISTOR BETWEEN INPUT TERMINALS DATA+ AND DATA- OF THE RS-485 REPEATER. INSTALL A 120 OHM,
1/4 WATT RESISTOR BETWEEN TERMINALS 7 AND 8 OF THE LAST S7810M MODBUS™ MODULE IN THE ADDITIONAL DAISY CHAIN.
LOCAL RS-485 COMMUNICATIONS BUS. THE DEVICES ON THIS BUS MUST BE WIRED IN A DAISY CHAIN CONFIGURATION. THE ORDER OF
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INTERCONNECTION IS NOT IMPORTANT. THE MODULES ON THE CLOSEST AND FARTHEST ENDS OF THE DAISY CHAIN REQUIRE A 120 OHM,
1/4 WATT TERMINATION RESISTOR BETWEEN TERMINALS 1 AND 2 OR A AND B.
THREE WIRE SHIELDED CABLE (BELDEN 8723 SHIELDED OR EQUIVALENT) IS RECOMMENDED AND SHOULD BE GROUNDED AS
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FOLLOWS: IF NO INTERFERENCE IS PRESENT, OR TO REDUCE CAPACITIVE INTERFERENCE, THE SHIELD SHOULD BE GROUNDED
AT ONE END. WHEN GROUNDING ONLY ONE END OF THE THE SHIELD, THE SHIELD END CLOSEST TO THE S7810M MODBUS™
MODULE SHOULD BE ATTACHED TO EARTH GROUND. TO REDUCE INDUCTIVE INTERFERENCE (RF INTERFERENCE), THE SHIELD
SHOULD BE GROUNDED AT BOTH ENDS.
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TERMINAL NUMBERS ARE ON 203541 5-WIRE CONNECTOR (SUPPLIED WITH REMOTE MOUNTING BRACKET).
NOTE: LED has been replaced by block characters visible on
the MB address setup menu.
PC/PLC GND
-
+ RS-485
BUS
A B C
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Fig. 8. Wiring for ModBus
7800 SERIES S7800A KEYBOARD DISPLAY MODULE
1 2 3 4
1 2 3 4
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1 2 3 4
1 2 3 4
6
TM
Feature.
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MOMENTARY
PUSHBUTTON
SWITCH
5
5
RM78xx SERIES DEVICE
WITH S7800 SERIES 5
OR GREATER DISPLAY.
MOMENTARY
PUSHBUTTON
SWITCH
5
5
RM78xx SERIES DEVICE
WITH S7800 SERIES 5
OR GREATER DISPLAY.
M24190
65-0090-6