Rockwell Automation 1775-S5_SR5,D17756.5.5 User Manual PLC-3 FAMILY I/0 - Manual (Page 155)

Binary Command Language
Appendix A
A-27
The data bytes store:
least significant byte of the address (48 hex)
second byte of the address (02 hex)
third byte of the address (01 hex)
most significant byte of the address (01 hex)
least significant byte of the size word (10 hex)
most significant byte of the size word (00 hex)
The processor response to a read block physical command is the same as
the response to a read block command (see “Read Block Command,
page A-18).
When uploading to a computer, you need to know how much memory is
actually used. You can find the address of the last word used in memory
with the following algorithm:
1. Read words 35 and 36.
2. Use the least significant byte of word 35 plus word 36 as the three
least significant bytes in a physical address.
3. Subtract 9 from the physical address in step 2.
4. Read 2 words starting from the result of step 3.
5. The least significant byte of the first word plus the second word read
in step 4 contain the three least significant bytes of the physical
address of the last word used in memory (Figure A.4):
Figure A.4
Finding the Address of the Last Used Memory Word
Result of step Word 35 Word 36 Description
1 1101100000000000 0000000001101001 ---------
2 0000000100000000 0000000001101001 Points to word 105
3 0000000100000000 0000000001100000 Points to word 96
4 1000001100000001 0000000001000000 Contents of words 96 and 97
5 0000000100000001 0000000001000000 Points to word 65600 (the last
unused memory word)
Although uploading does not require a complete shutdown of the
processor, memory must not be created or deleted during the upload
operation. Therefore, be sure that no scanner or other module is creating
or deleting memory, and making changes in LIST during an
upload operation.