1747-6.22, Backup Scanner User Manual

Programming Techniques
Chapter 9
Chapter Objectives Read this chapter to familiarize yourself with techniques used to
program your SLC 500 backup system.
In this chapter we describe:
• how to get started with a program to transfer data table values
• two methods you can use to program the SLC 500 backup
system to transfer data table values
• the behavior of specific instructions when used in your
application program, and give you suggestions for dealing with
these instructions.
Getting Started The 1747-BSN modules control switchover and transfer remote I/O
data without additional programming. However, if you want to
transfer data table values from the primary to the secondary
processor, you must provide a ladder program. The following figure
shows the minimum ladder programming you must provide to
transfer 2 Kwords of the data table between the two 1747-BSN
modules, and to provide 1747-BSN module status. This program
constantly transfers data as fast as possible. 2K words is the
maximum per BSN module on the HSSL. With no local I/O, a 5/02 or
later processor supports up to 8 BSN modules for a maximum of 16K
words of retentive data transfer from primary processor to secondary
processor. Refer to the following section, Data Transfer Schemes, for
alternative approaches. You need to put this program in both
processors.
Publication 1747-6.22