HBM PW15iA, Инструкция по монтажу, Страница: 30 / 104

Interfaces
28
A4359-1.0 HBM: public
PW15iA
nect as many as 90 digital load cells to an RS-485 inter­
face. All the load cells are connected in parallel on a line,
the total length of the line can be as much as 500m. The
software uses the different addresses to differentiate
between the load cells. If the control computer only has
an RS-232 interface, an interface converter is required
(e.g. from HBM, ordering no.: 1-SC232/422B).
Bus termination Bus termination
TB
TA
RB
RA
PC = Master Node 1 Node 90
...
500
Ω
500
Ω
500
Ω
500
Ω
500
Ω
500
Ω
500
Ω
500
Ω
+5 V
+5 V
+5 V
+5 V
TxD on/off RxD
TB TA
T
R
RB RA
TxD on/off RxD
TB TA
T
R
RB RA
TxD on/off RxD
TB TA
T R
RB RA
Fig. 5.1 Connecting several nodes to a PC via an RS‐485
4‐wire bus
The correct assignment of the transmit and receive lines
can be seen in Fig. 5.1 (bus line Ra to Ta of the con­
verter, etc.). The PW15iA already includes bus termina­
tion resistors (line termination), that can be activated with
the software command
STR . So no additional bus termi­
nation resistors are required for RS-485.