Rockwell Automation 1747-BSN Backup Scanner Module - Manual (Page 158)

Publication 1747-UM010B-EN-P - September 2003
9-16 Programming Techniques
Data Transfer Method 2
With method 2, the application program in the SLC 5/0x considers
each data block independent from the other data blocks. This is
shown in the ladder program example earlier in this chapter for one
set of 1747-BSN modules. Reproduce this logic for additional sets of
1747-BSN modules, being sure to update the slot number in the M-file
addresses for each set. The following procedure is used in the primary
SLC 5/0x for sending the data blocks:
1. Read all the DTSWs from the respective 1747-BSN modules.
2. Clear all DTCW bits corresponding to the data blocks that are
marked as already transferred to secondary system in the
DTSWs. Send the data blocks to their respective 1747-BSN
modules.
3. For each data block, do the following:
•
Check whether the block is free to receive new data from the
SLC 5/0x.
•
Copy the data block from the SLC 5/0x to the 1747-BSN
module.
•
Advise the 1747-BSN module that the data block is ready
through the DTCW (set the bit corresponding to the data
block in this word).
4. Start step 1 in the next program scan.
To receive the data blocks, the secondary SLC 5/0x application
program uses the procedure below:
1. Read all the DTSWs from the respective 1747-BSN modules.
2. Clear all DTHW bits corresponding to the data blocks that were
previously read and that no longer have a data ready bit set for
them in the DTSWs. Send all the DTHWs to their respective
1747-BSN modules. For each data block, do the following:
•
Check whether the data block is ready in the 1747-BSN
module.
•
Copy the data block from the 1747-BSN to the SLC 5/0x.
•
Advise the 1747-BSN module that the data block was already
read through the DTHW (set the bit corresponding to the data
block in this word).
3. Start step 1 in the next program scan.
The worst scenario with this transfer method is a system with eight
1747-BSN modules in which each one is transferring 16 data blocks.