Communication
2.3 Modbus RTU Master
87SICAM Q100, 7KG95xx, System Manual
E50417-C1040-C522-A8, Edition 09.2020
Supported Modbus Functions
The Modbus RTU Master of SICAM Q100 supports the following Modbus functions:
Support of Modbus Slave Devices
The Modbus RTU master supports 8 Modbus slave devices each with:
• 15 readable measured values per Modbus slave device
• 6 readable indications from each Modbus slave device
Properties of the Modbus RTU Master
• Master-Slave protocol
• 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 is used as interface.
• The Modbus RTU message has a maximum size of 256 bytes:
1 byte server address
253 bytes for data
2 bytes for CRC
Table 2-66 Supported Modbus RTU Master Functions
Function
Number
Function Name Description
01
(0x01H)
Read Coil Status Reading one or several coil status registers of a Modbus slave
02
(0x02H)
Read Discrete Inputs
(Read Input Status)
Reading one or several input status registers of a Modbus slave
03
(0x03H)
Read Holding Registers Reading one or several holding registers of a Modbus slave
04
(0x04H)
Read Input Registers Reading one or several input registers of a Modbus slave
NOTE
If more than the specified number of measured values and/or indications have to be read by a Modbus slave
device, it is possible to assign the same address to multiple devices when configuring the devices connected
to the Modbus master in SICAM Q100. The data of all devices with the same address are then queried by a
Modbus slave device.
SYS_SICAM_Q100_US.book Page 87 Thursday, September 24, 2020 1:17 PM
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