Download BT 1050 Technical information

Front
Slave(s)
(Boiler controller)
COM SCN Tx-
E
Tx+ Rx- Rx+ H / D H / D
97 96 95 94 93 92 91 90
A
R*
rc
hi
ve
Add link between
terminals 91 and 90
Common
R*
Earth*
* See wiring notes
Rx
Tx
Master
Fig. 8 RS485 / Modbus half duplex circuit (view from the top)
EIA / TIA-485 wiring notes continued:
-
The bus common must be connected directly to protective ground / earth at one point only.
Generally this point is at or near the master device.
-
Consider terminating the two furthest ends of the bus to match the transmission line
impedance. A 150 ohm (0.5 W) resistor or a 120 ohm (0.25 W) resistor, which is decoupled
with a 1 nF (10 V) capacitor is commonly used, but ideally the line impedance should be
matched to each individual installation. Termination for short lengths of cable should not
be necessary < 300 m (< 1 000 ft) @ 9 600 Baud.
-
See 'Technical information' for cable details.
IM-P405-39 AB Issue 1
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