Rockwell Automation 1771-QC , D17716.5.25 SER/B SERVO POS - Manual (Page 86)

Formatting and Interpreting Data Blocks
Chapter 7
7Ć4
moves would have to use the global accel/decel and final rate values from
the parameter block.
Upon request from the status block, the PC processor sends a moveset
block to the 1771-M3 controller, which transfers each move description to
the 1771-ES expander one at a time. The 1771-ES expander generates the
analog voltage to command axis motion as programmed.
Command Block
The command block for a 1-axis system has up to four words; a 2-axis
system has up to eight words; a 3-axis system has up to 12 words. This
block regularly transfers from the data table to provide commands (such
as start, slide stop, search home, jog, reset and offset) for each axis unless
the 1771-M3 controller needs a parameter or moveset block. You must
include the command block address in the parameter block.
Data Table Allocation
You must allocate a sufficiently large data table area for the data blocks
needed in the block transfer communication. Furthermore, the parameter
block must start at least 63 words before the end of a contiguous data
table area. Also, each moveset block (regardless of size) must start at
least 64 words before the end of a contiguous data table area. For a
PLC-2 family processor, assign data block addresses of 200 or greater to
avoid processor work areas.
The status block, which is the only block transferred from the 1771-M3
controller to the processor, contains information about axis and servo
positioning assembly status. The first block transfer after power-up writes
a 6-word status block into the data table. After that, the status block
consists of word assignments (Figure 7.2):
Number of Axes
Size of
Status Block
1 6 words
2 10 words
3 14 words
Status Block