Read and Write Zones

The Zones

Within the application memory, the I/O scanning service defines:

%MW word zone: reserved for reading inputs
%MW word zone: reserved for writing outputs
refresh periods: independent of the PLC scan

The read and write zones associated with the Ethernet module are tables of internal words (%MW) that contiguously group all input and output word values for connected remote devices. Remote input and output devices are supplied with:

input words: used to send back the values of the inputs to the module
output words: used to assign the value of the outputs to the remote device

NOTE: Refer to the documentation for each device for the number and details of input and output words to be managed.

Example

In this example, the Ethernet module scans three devices:

a Momentum module at address IP1 (type 170 AA1 140 00: 16 analogue inputs; this module has 16 input words and 4 output words)
a Momentum module at address IP2 (type 170 AA1 340 00: 16 discrete inputs; this module has one input word)
a Premium PLC with 125 input words at address IP3

The read zone begins at %MW100 and the write zone at %MW400.

NOTE: The fields dedicated to remote devices must not have any overlap. Equally, the read and write zones must not have any overlap.

NOTE: Not all devices can be write-scanned by multiple modules. Check the remote device’s documentation to see if it can be accessed by the I/O Scanner.