Data Structure; Communication Sequence; Unigate ® As Modbus-Ascii Master; Protocol „Universal Modbus Rtu Slave - DEUTSCHMANN AUTOMATION UNIGATE CL-CANopen Instruction Manual

Deutschmann Automation GmbH & Co. KG Implemented protocols with Universal Script - protocols application

11.4.3.2 Data structure

11.4.3.3 Communication sequence

The gateway always acts as the Slave with respect to the fieldbus and also acts as Slave at the
Modbus end. A data exchange is always initiated by the MODBUS-Master via the RS-interface. If
the Modbus-address (1st Byte) which is sent out by the Modbus-Master is identical with the
address set on the gateway, the gateway sends the received data (without Modbus-address and
CRC-check sum) to the fieldbus-master (look picture above). With it the gateway optionally com-
pletes as an introduction a Trigger byte and a Length byte.
The fieldbus-master detects when it has to analyse a record via the Trigger byte which is incre-
mented by the gateway at every inquiry. The number of the following Modbus-data is to be found
in the length byte.
Now the fieldbus-master has to analyse the Modbus-inquiry and it has to send back the answer
in the same format (optionally with the leading Trigger byte and Length byte) via the fieldbus to
the gateway.
The gateway then takes this answer and completes the Modbus-address and the CRC and
sends the data to the Modbus-Master via the RS-interface. With it the data exchange is com-
pleted and the gateway waits for a new inquiry from the Modbus-Master.
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11.4.4 UNIGATE
-> For the description see chapter 11.4.2 "UNIGATE® as MODBUS-Master"
11.5 Protocol „Universal Modbus RTU Slave"
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The UNIGATE a Modbus slave on the application side. The slave ID is set with the rotary
is
coding switches S4 + S5 (S4 = High, S5 = Low).

11.5.1 Data structure on the fieldbus side e.g.: PROFIBUS

Applies to In and Out
1. Byte: trigger byte, optional (see chapter 14, The trigger byte)
2. Byte: fieldbus length byte, optional (see chapter 15, The length byte)
3. Byte: process data
4. Byte: process data
....
23.2.22
as Modbus-ASCII Master
UNIGATE fieldbus gateway UNIGATE
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