Implemented protocols in UNIGATE® CX
Deutschmann Automation GmbH & Co. KG
26
UNIGATE
®
CX V. 1.4
2.10.19
7.5.3
UNIGATE
®
as MODBUS-Slave
7.5.3.1
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.
Since the Modbus operates with a variable data format - dependent on the required function and
data length - but since the fieldbus requires a fixed data length, this must be preset by means of
a selection in the GSD file. This length should be selected by the user such that the longest Mod-
bus request resp. response can be processed.
7.5.3.2
Data structure
7.5.3.3
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.
7.6 Protocol Modbus ASCII Master/Slave
The fieldbus data exchange for Modbus ASCII is identical with RTU. On the serial site the
UNIGATE automatically transfers the data in ASCII format.
-> For the description see chapter 7.5.2, UNIGATE® as MODBUS-Master respectively see chap-
ter 7.5.3, UNIGATE® as MODBUS-Slave.
7.7 Protocol „Universal Modbus RTU Slave“
The UNIGATE
®
is
a Modbus slave on the application side. The slave ID is set with the rotary
coding switches S4 + S5 (S4 = High, S5 = Low).
Summary of Contents for UNIGATE CX Series
Page 2: ...Manual Art No V3792E...
