Rockwell Automation 8520 9/Series CNC Integration Maintenance Manual Documentation Set - Manual (Page 281)

Section 5A
9/440 Resolver--based CNC/Drive System
5A-35
ATTENTION: The E--Stop status relay (or your
customer--supplied E--Stop control relay) should not be the only
method through which axis brakes are directly released (see the
illustration below). Brakes should be released by a combination
of the PAL logic when it determines that the 9/440 system is in
full control of the servo motors and the control’s E--Stop status
contact and an external hardware E--Stop contact. Refer to the
description of the PAL flags $AXME and $STME for details
about testing drive status.
Power
Supply
Brake
PAL--controlled
9/440 E--Stop
Status Relay