B&B Electronics VFG3000 - Manual - Manual (Page 37)

C ONFIGURING C OMMUNICATIONS D ATA T RANSFORMATION
R EVISION 1 P AGE 21
To move data between two master devices, simply select one of the devices, and create a
Gateway Block for that device. You can then add references to the other device’s registers
just as you would when exposing data on a slave protocol. Again, C2 will automatically read
or write the data as required, transparently moving data between the devices. The example
above shows how to move data from a Mitsubishi FX into an SLC-500.
W HICH W AY A ROUND ?
One question that may occur to you is whether you should create the Gateway Block within
the Allen-Bradley device, as in this example, or within the Mitsubishi device. The first thing
to note is that there is no need to create more than a single block to perform transfers in a
single direction. If you create a block in AB to read from MITFX, and a block in MITFX to
write to AB, you’ll simply perform the transfer twice and slow everything down! The second
observation is that the decision as to which device should “own” the Gateway Block is
essentially arbitrary. In general, you should create your blocks so as to minimize the number
of blocks in the database. This means that if the registers in the Allen-Bradley lay within a
single range, but the registers in the Mitsubishi are scattered all over the PLC, the Gateway
Block should be created within the Allen-Bradley device so as to remove the need to create
multiple blocks to access the different ranges of the Mitsubishi device.
D
ATA
T
RANSFORMATION
You may also use Gateway Blocks to perform math operations that your PLC might not
otherwise be able to handle. For example, you may want to read a register from the PLC,
scale it, take the square root, and write it back to another PLC register. To accomplish this,
refer to the section on Data Tags, and create a mapped variable to represent the input value
that will be read from the device. Then, create a formula to represent the output value, setting
the expression so as to perform the required math. You can then create a Gateway Block
targeted at the required output register, and drag the formula across to instruct Fieldbus
Gateway Manager to write the derived value back to the PLC.