8 Communication
8.2 Modbus
143
SICAM I/O Unit, 7XV5673, Device Manual
E50417-H1040-C484-A3, Edition 05.2012
8.2.5
Modbus RTU
Properties of the Modbus RTU
•
Client-server protocol
•
All clients have a unique address in the range from 1 to 247.
•
Packets with the address = 0 are forwarded to all clients (broadcast).
•
The individual data bytes in the messages are transmitted asynchronously with 11 bits.
−
1 start bit,
−
8 data bits,
−
1 parity bit and 1 stop bit or
−
no parity bit and 2 stop bits
•
Single messages are separated by bus silent intervals of at least 3.5 character times and end with a CRC
code for error detection.
•
RS485 or FO is used as bus physics.
•
The Modbus RTU data packet has a maximum size of 256 bytes.
−
1 byte server address
−
253 bytes for data
−
2 bytes for CRC
The following parameters can be set for the Modbus RTU:
Table 8-4
Modbus RTU Settings
Parameter
Default Setting
Settings
Device address
1
1 to 247
Baud rate
19 200 bit/s
1200 bit/s
2400 bit/s
4800 bit/s
9600 bit/s
19 200 bit/s
38 400 bit/s
57 600 bit/s
115 200 bit/s
Parity
Even
Even
Odd
None, 1 stop bit
None, 2 stop bits
Access rights
Full
Full
Read only
Communication supervision time
600 * 100 ms
0 s = none
100 ms to 6 553 400 ms
MAN_SICAM_IO-Unit_7XV5673_US.book Page 143 Thursday, May 10, 2012 10:59 AM