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6. Configuring the Gateway
Field in the
frame
Size in the
frame
Description
Slave
Address
1 byte This field cannot be changed by the user and its value is greyed out to inform
him of the fact. AbcConf updates the value of this field automatically using the
address of the Modbus slave corresponding to the current node.
N.B.: This field is common to queries for all Modbus commands.
E.g.: The value of this field is set to the address of the Modbus slave which
corresponds to the “ATS48” node, that is to say to 16#0A.
Function 1 byte This field cannot be changed by the user and its value is greyed out to inform
him of the fact. AbcConf updates the value of this field automatically using the
function code for the corresponding Modbus command.
N.B.: This field is common to queries for all Modbus commands.
E.g.: The value of this field is set to the code for the “Preset Single Register”
command (writing the value of an output word), that is to say 16#06.
Register 2 bytes
Address of an output word, or of a register, in the Modbus slave’s memory. So this
field designates the memory object to which the command relates.
N.B.: This field is common to queries for all Modbus commands whose
purpose is to access one or more locations in the memory of a Modbus slave.
When accessing several memory locations, the “Register” field designates the
address of the first word affected by the command.
E.g.: The value of this field should be changed by entering the address of the
CMD command register, that is to say 400 (16#0190). This value will be
automatically converted to hexadecimal if the user enters it in decimal.
Preset Data 2 bytes
or more for a
block of data
Data Location: Address, in the gateway’s output data memory (16#0202 to
16#02F3), of the item of data to be transmitted in the “Preset Data” field for the
query’s frame.
N.B.: The “Data location” field is used for each frame that allows you to
exchange some data between the Modbus slaves and the Profibus-DP master.
In this case it designates the starting address of the block of data to be
transmitted.
N.B.: As far as possible, ensure that the data is located at even addresses in
order to align the Modbus data (in 16-bit format) on the QW4.0.x outputs of the
Profibus-DP coupler.
E.g.: The value to be assigned to the ATS48’s CMD register should be placed
in the gateway’s output data memory area. We will be using the first free
location starting at an even address, that is to say the one located at 16#0220,
with the gateway’s default configuration.
Data length: Length of the block of output data, in the gateway’s memory,
whose values must be transmitted in the “Preset Data” field of the query’s
frame. It is expressed in number of bytes.
N.B.: The “Data length” field is always used together with the “Data location”
field, described above.
E.g.: Since the “Preset Single Register” command is used to write the value of a
single register (16-bit), the value of the “Data length” field must be set to 2.
See the documentation for each Modbus slave to find out the maximum
amount of 8-bit data which can be placed in “Data” type fields in queries and
responses for this slave. With the ATS48, for instance, it is limited to 30 16-bit
words.