5
MULTIMODULE 133
TECSYSTEM S.r.l ®
7) DATA TRANSMISSION ON MODBUS NETWORK
MULTIMODULE 133 module allows to connect NT133 monitoring unit with a RS485 net-
work with ModBus RTU protocol in order to read the data shown in table 16 and to write
the ones shown in paragraph 13.
The module is always in slave mode.
NT133 monitoring unit appears to be connected with the network only when it is in tem-
perature reading mode and not when it is in programming or programming display.
In case NT133 is not properly connected with MULTIMODULE 133, led RX NT-x stays
fixed on. If a bad data transfer between NT133 and MULTIMODULE 133 should occur,
the same led blinks.
8) RS485 CONNECTIONS
As far as the signal cable to be used in order to ensure a proper network working is con-
cerned, we recommend to follow what laid down by EIA RS485 standard which suggest
to use a 24AWG duplex cable.
The duplex cable which connects all the units in RS485 needs the activation of the 120
ohm termination on the last unit of the series (please refer to SW2 page 17).
Connect the duplex cable paying attention to polarities and lay the network avoiding to
make sharp bends or ring windings in order to avoid the modification of line impedance.
If necessary, also the GND terminal for grounding is available.
9) DATA FRAME
The frame in asynchronous transmission is composed of: 1 start bit, 8 data bits, 1 parity
bit (even or odd, if the parity has been set, please refer to SW2 page 17) and 1 stop bit.
The available Baud rate are: 2400, 4800, 9600 and 19200.
The words length (DATA) is 16 bit where not specified.
10) DATA PACKET
A complete sequence of request/answer is composed as follows:
Master request:
SLAVE ADDRESS
- 1 byte
FUNCTION CODE
- 1 byte
DATA
- variable, it depends by function code
CRC
-
2
bytes
Slave answer:
SLAVE ADDRESS
- 1 byte
FUNCTION CODE
- 1 byte
DATA
- variable, it depends by function code
CRC
-
2
bytes
