Rockwell Automation GMLC Reference Manual - Manual (Page 764)

Publication GMLC-5.2 - November 1999
Using Block Transfers 727
Up to 30 sequential user variables, or cam table points, can be transferred
in any one block transfer using 32-bit Signed BCD numeric format,
because each block transfer is limited to a maximum of 64 words, as
shown by the following formula:
If the PLC is getting data from the motion controller, no data values need
be specified in the BTW data file and thus the end-of-block delimiter is
word 3 (nn = 0). The data returned by the BTR is stored in the BCD (D)
file specified in the BTR. After completing the BTR, this file contains the
returned values, as shown below.
The returned values are stored in word pairs 0, 1 through 2nn – 2, 2nn – 1
(where nn is the number of items read) in signed BCD format. The most
significant word of the returned value is stored in the lower numbered
word of the data file and the least significant word of the returned value in
the higher numbered word. Since each 32-bit value is stored as two 16-bit
words, 2nn + 1 words in the data file are used.
RIO Adapter Block Transfer Read
32-bit Signed BCD Format
Returned Values Data File Format
Word Description
0
1 First Data Item Value Most Significant Word
First Data Item Value Least Significant Word
2
3 Second Data Item Value Most Significant Word
Second Data Item Value Least Significant Word
2 nn-2
2 nn-1
Last Data Item Value Most Significant Word
Last Data Item Value Least Significant Word
2 nn End-of-Block Delimiter (000D Hex)
30 Items 2
Words
Item
----------------
×
3 Header Words End-of-Block Word
64 Words =
+ +