SATK22
20
Modbus
The HIU offers a remote connectivity solution by means an
RS-485 wired network and Mod-Bus communication protocol.
On request, Altecnic will supply a map of the Mod-Bus registers
and data transmission specifications so the product can be
integrated in an existing BMS system.
The RS-485 communication network should be preferably
constructed in compliance with the prescriptions of standard
EIA RS-485
.
Any other configuration of the physical layer is at the discretion
of the BMS system operator, which will assume responsibility
for checking the implications in terms of transmission quality.
In particular, it is essential to use a two-wire twisted cable.
Compliance with this requirement becomes even more
significant the more extensive the RS-485 network.
If, alternatively, a shielded wire is used, the shield must be
connected solely on the master side.
As a guideline, take account of the following general
prescriptions to ensure optimal transmission quality:
•
use a BUS cable with impedance of around 120 Ohm;
•
connect a terminal resistor, having same impedance as the
cable, at each end of the RS-485 cable;
•
keep the length of side branches as short as possible.
The device is configured by default to support a
communication speed of 9600 baud/s with parity “none”.
The communication speed can be changed via Modbus, to the
following values: 2400, 4800, 9600, 19200 baud/s.
To the ModBus
master
RS-485
MASTER
IN / OUT
SLAVE # 1
IN / OUT
SLAVE # n
IN / OUT
CHARACTERISTIC
IMPEDANCE = Z
0
TERMINATING
RESISTOR
R
T
=Z
0
TERMINATING
RESISTOR
R
T
=Z
0
KEEP AS SHORT AS POSSIBLE
