20
NT210 K
INTRODUCTION TO THE MODBUS INSIDE MODULE
The MODBUS INSIDE expansion module is embedded in the control unit and allows transferring data on an RS485
network with MODBUS RTU protocol.
OPERATING NOTES
For the module to work correctly, the set-up parameters of the RS485 network must be set: address, baud rate, parity bits.
See programming steps 28 to 33 as shown in the table on page 18.
The serial communication of the temperature control unit is active only when the NT210 K is in temperature control
mode in one of the modes provided (Scan, Man and T.Max).
When other functions such as programming, programming display and relay test are activated, the ModBus
communication is temporarily disabled.
DATA TRANSMISSION ON MODBUS NETWORK
The MODBUS INSIDE internal module allows connecting the NT210 K control unit to an RS485 network with ModBus
RTU protocol. In order to read/write data remotely, read the paragraph notes for remote programming on page 21.
Note: the module is always in slave mode.
The NT210 K control unit communicates with the network only when it is in temperature reading mode, while it is inactive
when it is in the following modes: display, programming and relay test.
RS485 ELECTRICAL CONNECTIONS
As to the signal cable to use in order to guarantee correct network operation, follow standard EIA RS485 that
recommends the use of a 24AWG pair.
The pair that connects all the units in RS485 might require a 120 ohm terminating resistor on the last unit of the series.
Connect the pair taking polarities into account and lay the network avoiding to create tight bends or ring windings so as not
to change the line impedance. Place always the cable away from the power cable.
If necessary, the terminal for the GND earth connection is available.
DATA FRAME
The frame in asynchronous transmission consists of: 1 start bit, 8 data bits, 1 parity bit (even or odd if parity has been
set) and 1 stop bit.
The allowed Baud rates are: 2400, 4800, 9600, 19200, 38400.
Where unspecified, the length of the words (DATA) is 16 bits.
DATA PACKET
A complete sequence of request/answer consists of the following: Master request:
SLAVE ADDRESS
- 1 byte
FUNCTION CODE
- 1 byte
DATA
- variable, depends on the function code
CRC
- 2 bytes
Slave request:
SLAVE ADDRESS
- 1 byte
FUNCTION CODE
- 1 byte
DATA
- variable, depends on the function code
CRC
- 2 byte
MODBUS RS485 OUTPUT OPTION
