Rockwell Automation 8520-ARM2 9/Series CNC AMP Reference Manual Documentation Set - Manual (Page 653)

Miscellaneous Parameters
Chapter 37
37-13
Function
Use this parameter to determine the maximum number of motion blocks
that may be retraced using the block retrace feature. The block retrace
feature is used to reverse execution of an active program. The control
executes blocks in reverse order and reverse direction up to the maximum
number of retractable blocks set with this parameter. Press the
START> button to return the program to normal forward execution.
Important: There are restrictions as to the type of blocks that may
be retraced. Refer to your programming and operation manual for more
information.
Axis Parameter Number
Single Process Process 1 Process 2
All [9] [20009] [21009]
Range
1 to 15 blocks (see Notes)
Notes
It is important to keep the value of block retrace limit as small as possible.
The number of retrace blocks is directly affected by the number of look
ahead blocks that the control has available for processing. The control will
delete retrace blocks as needed to maintain its minimum number of look
ahead blocks. Keeping this value small helps increase the control’s
efficiency by always leaving enough memory available for block look
ahead. Refer to your operation and programming manuals more
information.
Important: Some system configurations will have less than 15 retrace
blocks available to them. The exact number depends on your hardware
configuration, the number of axes on the system, the options activated, and
the revision of the system executive. If you configure more retrace blocks
than are available at any given time on your system, the error message
“A RETRACE BUFFER WAS DELETED” is displayed while a part
program is executing. This error message indicates that the control has
deleted one (or more) of the block retrace buffers and can no longer retrace
as many part program blocks as you originally specified in AMP.
37.13
Block Retrace Limit