Introducing the PLC2/DHII Interface
Chapter 2
212
Figure 2.6
Write with No Reply Message Transfer
Node
1
Node
2
Command Message — Block of data
to write into host at Node 2
Figure 2.7
Write with Reply Message Transfer
Node
1
Node
2
Command Message — Block of
data to write into host at Node 2
Reply Message — Status of
whether the write was successful
If the local node host transmits a command to write verified, the local
node interface first transmits a command to write with reply. When the
remote node interface receives the token, it transmits a reply message to
indicate whether it was able to successfully write into the host’s memory.
When the local node interface receives the token again, it then
automatically transmits a command to read that same block of data. After
the remote node interface writes the data into its host’s memory, it reads
that data from the host’s memory. When the remote node receives the
token, the remote node interface then transmits this data back to the local
node. The local node interface then verifies that the data it received is
identical to what it had transmitted (Figure 2.8)
