Allen-Bradley controllogix 1756-L61, Application Book

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49 Publication LOGIX-AP007B-EN-P - January 2007
Appendix
D
Expand the Code to Support More than 4500
Bytes of Data
Introduction
This appendix describes how to expand the code to support more than 4500
bytes of data.
Modify the Application to
Access More Data
The baseline application supports reading or writing 4500 bytes of data to
CompactFlash card. If you need to access more data, modify the baseline
application.
For example, you might have three groups of data that you want to write to the
CompactFlash card. One group will be 250 bytes, one will be 3000 bytes, and
the last will be 10,000 bytes. The first two will not warrant any changes to the
baseline application, but the last will. You will need to expand three tag’s array
sizes.
Before writing to the CompactFlash card, calculate how big to make those
three arrays. Do not increase them to 10,000 bytes. Be sure to take into
consideration that of the 450 bytes, 8 bytes are checksum information, leaving
442 bytes for user data.
Step 1:
Actual_Bytes_to_RW = Bytes (TRN (Bytes_to_RW/442) * 8) + (If
the MOD (Bytes_to_RW/442) > 0 then 8 else 0)
Step 2:
450 [TRN(Actual_Bytes_to_RW/450) +(if the MOD (Actual_Bytes_to_RW)
> 0 then 1 else 0]
Topic Page
Modify the Application to Access More Data 49
Access 10,000 Bytes Example 50
Modify the Arrays 51
Modify the Data Element 51