Communication Sequence; Unigate; Preparation; Data Structure - DEUTSCHMANN AUTOMATION UNIGATE CL-Fast Ethernet Instruction Manual

Implemented protocols in UNIGATE® CL with Universal Script

10.4.2.3 Communication sequence

The gateway always acts as the Slave with respect to the fieldbus and always acts as the Master
at the Modbus end. Thus, data exchange must always be started by the fieldbus Master. The
gateway fetches this data which must be structured in accordance with chapter "Data structure",
from the fieldbus Master, determines the valid length of the Modbus data if the length byte is not
activated, adds the CRC checksum and sends this data record as a request on the Modbus.
The response of the selected Slave is then sent to the fieldbus Master by the gateway - without
CRC checksum. If no response occurs within the stipulated "Response time", the gateway sig-
nals a "TIMEOUT ERROR".
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10.4.3 UNIGATE

10.4.3.1 Preparation

Before data exchange is commenced, the parameters "Trigger byte" and "Length byte", "Baud
rate", "Parity", "Start bits", "Stop bits" and "Data bits" must be set.
At the rotary switch on the RS-side the MODBUS-ID has to be set, under which the gateway is
addressed in the Modbus.

10.4.3.2 Data structure

10.4.3.3 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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10.4.4 UNIGATE
On request!
-> For the description see chapter 10.4.2 "UNIGATE® as MODBUS-Master"
26 UNIGATE

as MODBUS-Slave

as Modbus-ASCII Master

Fieldbus Gateway UNIGATE
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Deutschmann Automation GmbH & Co. KG
CL - Fast Ethernet V. 2.6
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21.6.18