User manual for - TEMPERATURE TRANSDUCER TRS-02a
5.
PRINCIPLE OF OPERATION
module is equipped with IC analog to digital converter of 16 bits resolution.
Converted measurement signals are transmitted to the microcontroller where they are
computed and filtered according to given parameters. Measurement data can be readed from
the module via RS-485 interface by any MASTER controller (i.e. Control panel or PC). In
factoring process, the same address (0xFE) is written to every module. These addresses can
be changed at any time using proper MODBUS commands, or can be forced to be reset to
0xFF value using module internal momentary switch (to enhance system installation process,
see:
FORCING OF 0xFF ADDRESS
). All settings are stored in non-volatile EEPROM memory,
and available under fixed register numbers.
LED indicator is installed in the module mainboard, it indicates following situations:
•
normal operation mode
- flashes every about 2 second.
•
handmade forcing of address
0xFF
- permanent light
6.
THE MODBUS PRO
TOCOL HANDLING
Transmission parameters:
1 start bit, 8 data bits, 1 stop bit, no parity control
Baud rate:
9600 bits/second
Transmission protocol:
MODBUS RTU compatible
The device parameters and measurement result are available via RS-485 interface, as
HOLDING-type registers of Modbus RTU protocol. The registers (or groups of the registers)
can be read by 03h function, and wrote by 06h (single register only) accordingly to Modbus
RTU specification. Maximum group size for 03h function can not exceeds 5 registers (for single
frame).
The device interprets the broadcast messages, but then do not sends the answers.
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