10
IE-SNC-T83(4)48-03
Description of communication protocols
Detailed description of each communication protocols including examples
of communication is available in individual document “
Description of
communication protocols”
which is available at
www.cometsystem.cz
(see
appropriate transmitter pages).
Note:
After switching on the power of the device it can last up to 2 s
before the device starts to communicate and measure!
Modbus RTU
Control units communicate on master-slave principle in half-duplex
operation. Only master can send request and only addressed device
responds. During sending of request no other slave station should respond.
During communication, data transfer proceeds in binary format. Each Byte
is sent as eight bit data word in format: 1 start bit, data word 8 bit (LSB
first), 2 stop bits (device sends two stop bits, for receive one stop bit is
enough), without parity. Device supports communication speed from 110Bd
to 115200Bd.
Sent request and response have syntax:
ADDRESS OF DEVICE
– FUNCTION – Modbus CRC
Supported function
03 (0x03)
: Reading of 16-bit registers (Read Holding Registers)
04 (0x04)
: Reading of 16-bit input gates (Read Input Registers)
16 (0x10)
: Setting of more 16-bit registers (Write Multiple Registers)
Jumper and button
If communication protocol Modbus is selected the function of jumper and
button is as follows:
Jumper opened
– device memory is protected from writing, from device
side it is only enabled to read measured value, writing to memory is
disabled (no change of device address, communication speed and LCD
setting is enabled
…)
