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Manual -MD150T – 27.10.2014 – v.1.3
page 11
7.
USB and RS485 MODBUS interfaces
7.1
USB interface
USB interface is used for communication of MD150T process display with MD150-PC software (device
configuration, recording of measurements) and for updating of internal software. MD150 process
display must be powered in order to facilitate communication via USB.
Caution!
USB interface is prone to interference in the power supply grid and to electromagnetic
interference occurring in industrial environments. In case of connection problems during
communication of the digital processing unit with MD150T-PC software, apply additional
protective elements in the form of:
Powering of MD150T digital processing unit from an independent power supply source,
Application of network filters upstream of the indicator supply feeder.
Use of USB cable of length <1,5m equipped with ferrite beads at the cable beginning and its end.
Use of optically insulated USB hubs at PC side.
In
t
he conditions of severe interference (e.g. high interference of power grid) the communication may not
be possible.
7.2
RS485 (MODBUS-RTU) interface
MD150T digital processing unit is equipped with RS485 interface. It can be used for communication
with PLC controller, HMI panel or other device supporting MODBUS-RTU protocol. Default
transmission parameters:
Speed:
38400bps
, Bits: 8, Stop Bits: 1, parity: none
Address
Modbus: 1
Transmission speed and MD150T digital processing unit address in MODBUS-RTU network can be set
with the following parameters:
13. ADR
-
speed setting MODBUS (9600, 19200, 38400, 57600, 115200)
14. BAUD
-
address setting MODBUS (1…99)
7.2.1
Description of MODBUS protocol
Implemented functions MODBUS
Function no(hex)
Description
1 (0x01)
Reading of outputs status (relays)
3 (0x03)
Reading X registers
5 (0x05)
Recording of single Bit
Type of variables used
Name
Description
Size
(Bytes)
Number of occupied registers
DINT
Complete number with a
sign
4
2
REAL
Floating point number
4
2
