Rockwell Automation 1771-DE Absolute Encoder Module User Manual - Manual (Page 28)

Module/Processor Communication
Chapter 4
4Ć4
Thewrite-data throughput time is the time between the end of a
block-transfer-write operation and the module update of its outputs. The
module’s response time can vary, depending on the number of outputs it
controls, the type of absolute encoder you use, and if you have an offset
value. The worst case is 4.7 ms. Use the following table to determine the
module’s response time in milliseconds for your application.
Type of Encoder (with or without offset)
BCD without offset 2 4 6 8
BCD with offset
Gray code or binary without offset
Gray code or binary with offset
1.2
2.0
1.3
1.9
1.8
2.9
2.0
2.6
2.5
3.8
2.6
3.4
3.1
4.7
3.3
4.1
The processor reads data from the module and transfers it to its data table
in two read-data words. The module sends only two read-data words in
any one block-transfer-read operation. The format of these words is
shown in Figure 4.2 and is described here:
Figure 4.2
Format of BlockĆtransferĆread Data
17 16 15 14 13 12 11 10 07 06 05 04 03 02 01 00
0
Output 7
Output 6
Output 5
Output 4
Output 3
Output 2
Output 1
Output 0
Code indicating which
preset is in non-BCD format
Non-BCD preset flag
Unused
Write-data-valid
Loss-of-input-power
Word 1
Word 2
Status of outputs
13070
Current Absolute Position (in BCD)
0
The upper byte of 1 indicates the status of the eight outputs controlled
by the module. The module sets each bit when the corresponding
output is turned on. Refer to Appendix D for details of these bits.
The format of the lower byte of word 1 (by bit) is:
WriteĆData Throughput Time
BlockĆtransferĆread Data