Unigate ® As Modbus-Slave - DEUTSCHMANN AUTOMATION UNIGATE CL - DeviceNet Instruction Manual

Implemented protocols in UNIGATE® CL with Universal Script Deutschmann Automation GmbH & Co. KG
The user can choose whether the fieldbus requests are forwarded to the Modbus in an
event-driven way (On Event) or on request (On Trigger).
The mode "Modbus request on demand" necessitates the first byte in the fieldbus containing a
trigger byte (see chapter 10.9). This byte is not transferred to the Modbus and serves only to start
a Modbus transmission. For this purpose, the gateway constantly monitors this trigger byte and
sends data to the Modbus only when this byte has changed. In the reverse direction (to the field-
bus), the gateway transfers the number of received Modbus data records in this byte, i.e. this
byte is incremented by the gateway after each data record.
If the "Length byte" is activated (see chapter 10.10), the gateway transfers only the number of
bytes specified there. The number of received Modbus data items is saved in the direction of the
fieldbus Master. The length always refers to bytes "Address" to "Dat n" (inclusive in each case),
always without CRC checksum.
10.4.2.2 Data structure
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 as MODBUS-Slave
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.
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 via the con-
figuration with WINGATE (blocklength fieldbus input and blocklength fieldbus output). This length
should be selected by the user such that the longest Modbus request resp. response can be pro-
cessed.
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26 UNIGATE fieldbus gateway UNIGATE CL - DeviceNet V. 2.8 29.6.20
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