HBK AED 9101D, Руководство по эксплуатации

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27
AED
CONNECTING INTERFACES AND I/OS
commands
STR1;TDD1;. If the bus termination DIP switch is set to off, the commands
will have no effect on the AED9101D, i.e. bus termination will remain switched off! For the
AED9201B, the bus command alone is sufficient.
Important
The termination resistors may only be activated at the end points of the interface cable. If
resistors are also activated in between, this will weaken the signal and anything from
interference to data transmission failure could result.
Wiring and bus termination are achieved via RS-485 in a similar way with the 2‐wire con­
nection, except that the RA and RB lines are missing. Their function is performed lines TA
and TB. Line TA/RA is also described as T/R and line TB/RB as T/R+.
RS-485 with 2-wire connection
TB/RB
TA/RA
Master Node 1 Node X
...
500Ω
500Ω
500Ω
500Ω
+5 V +5 V
TxD RxD
TB TA
T R
RB RA
TxD RxD
TB TA
T R
RB RA
TxD RxD
TB TA
T R
RB RA
GND GND
Fig. 7.2 Bus layout for a 2-wire bus with RS‐485