The Trigger Byte; The Length Byte; Protocol „Universal Modbus Rtu Slave - DEUTSCHMANN AUTOMATION UNIGATE MB - MPI Instruction Manual

Deutschmann Automation GmbH & Co. KG
8.6

The trigger byte

Since the data is always transferred cyclically on PROFIBUS, the gateway must detect when the
user wishes to send new data via the serial interface. This is normally done by the gateway com-
paring the data to be transferred via the PROFIBUS with the old data stored internally - data
exchange on change (data exchange -> On Change). In many cases however, this cannot be
used as the criterion, e.g. whenever the same data is to be sent. For this reason, the user can set
control of transmission via a trigger byte (data exchange -> On Trigger). In this mode, the gate-
way always sends (and only then) when the trigger byte is changed.
Accordingly, the application program in the control in Normal mode cannot detect whether the
gateway has received several identical telegrams. If Trigger-Byte mode is activated, the gateway
increments the trigger byte each time a telegram has been received.
The first byte in the PROFIBUS input/output data buffer is used as the trigger byte if this mode is
activated.
8.7

The length byte

The user can configure whether the transmit length is also to be stored as a byte in the input/out-
put data area (Fieldbus lengthbyte -> active). In transmit direction, as many bytes as specified in
this byte are sent. On reception of a telegram the gateway enters the number of characters
received.
8.8 Protocol „Universal Modbus RTU Slave"
®
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).
27.10.21
®
UNIGATE fieldbus gateway UNIGATE
Implemented protocols in UNIGATE® MB
®
MB - MPI V. 1.9 25