Download 6. Configuring the Gateway

6. Configuring the Gateway
3) Changing the location of the Modbus data received in the gateway’s memory: As the number of bytes read
(see previous step) has increased from 2 to 16, the Modbus data received must be placed at a different
location in the gateway’s memory, and the size of the memory occupied must also be adjusted appropriately.
If you are not certain how much of the gateway’s memory is currently occupied, select “Sub-Network” and
choose “Monitor” from the “Sub-Network” menu. The following window appears, allowing you to see how
much of the gateway’s memory is occupied.
To see which memory locations are occupied by data from the command you are interested in, all you have
to do is uncheck the box corresponding to the “Read Holding Registers” command from the “TeSys U n°2”
node, as shown above. We can see that the Modbus data received in response to this command occupy
2 bytes located from address 0x0004.
NOTE: The memory locations 0x0000 and 0x0001 are reserved (see chapter 5). So you will not be able to
place any Modbus data in these locations.
The sizes displayed above the graphics areas of this window (“In Area 32 bytes” and “Out Area 32 bytes”)
correspond to the total input and ouput sizes you must check under RSNetWorx (see point 6 on next page)
and configure for the DeviceNet scanner (see point 7).
If you wish to place the 16 bytes of Modbus data which will be received by the gateway for this command into
memory, once the changes have been made, we will have to move all the other input data by 14 bytes, which
may be tedious, or change the memory location of the block of data received. In the example described here,
we will be using the second solution, although the first solution is actually preferable, in principle, as it avoids
leaving any “holes” in the gateway’s memory, thus optimising the transfer of all of the data to the DeviceNet
master PLC. Furthermore, the 1747-SDN scanner can only exchange 32 input words with the master PLC.
Leaving “holes” of this sort in the gateway’s memory is therefore not recommended in cases of large
configurations.
So we will be placing the 16 bytes of data from address 0x0020 (32 in decimal), that is to say directly after the
input data for the gateway’s default configuration.
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