Reference Manual

Turbo PMAC/PMAC2 Software Reference
Turbo PMAC Global I-Variables 115
where T
f
is the filter time constant, and T
s
is the servo update time.
f
T
s
T
f
T
40Ixx


The filter time constant can be expressed in terms of Ixx40 by the following equation:
40Ixx1
s
T*40Ixx
f
T


Filter time constants can range from a fraction of a servo cycle (when Ixx40 ~ 0) to infinite (when Ixx40
~ 1). As with any low-pass filter, there is a fundamental trade-off between smoothness and delay.
Generally, when the filter is used, filter time constants of a few milliseconds are set. In an application
where multiple motors are executing a path, the same time constant should be used for all of the motors.
Example:
To set a filter time constant of 2 msec on a system with the default servo update time of 442 sec, Ixx40
can be computed as:
819.0
2442.0
2
40Ixx 


Ixx41 Motor xx Desired Position Limit Band
Range: 0 – 8,388,607
Units: counts
Default: 0
Ixx41 specifies the difference between the software position limits using desired position at lookahead
time and those using actual position at move execution time.
Turbo PMAC will check the motor desired position at lookahead time if bit 15 of Ixx24 is set to 1. If the
lookahead desired position is greater than (Ixx13-Ixx41), or less than (Ixx14+Ixx41), Turbo PMAC will
limit the desired position at this value, and either stop the program on the path at this point or continue the
program while saturating the motor position at this value, depending on the setting of bit 14 of Ixx24.
Turbo PMAC also checks the motor actual position at move execution time. If the actual position is
greater than Ixx13, or less than Ixx14, Turbo PMAC issues an Abort command, bringing the motors to a
stop, but not along the path. This checking is done even if Turbo PMAC is already stopping on the path
because lookahead desired position was exceeded.
The purpose of Ixx41 is to permit the lookahead desired position limit to operate, stopping or limiting the
program in a recoverable fashion, without also tripping the actual position limit and creating an
unrecoverable stop. If the two limits are the same, a slight overshoot during the deceleration for desired
position limit would trip the actual position limit. Ixx41 should be set slightly greater than the magnitude
of the largest following error expected when decelerating at the Ixx17 maximum deceleration rate.
Ixx42 Motor xx Amplifier Flag Address
Range: $000000 - $FFFFFF
Units: Turbo PMAC Addresses
Default: $0
Ixx42, if set to a non-zero value, specifies the address of the amplifier-enable output flag and amplifier-
fault input flag, independently of position-capture flags and overtravel-limit flags, for Motor xx. If Ixx42
is set to 0, Ixx25 specifies the address of the amplifier flags as well as the position-capture flags, and
possibly the overtravel-limit flags, for Motor xx. This maintains backward compatibility with older
firmware revisions in which Ixx42 was not implemented. Whether the address of the amplifier flags is
specified with Ixx25 or Ixx42, the polarity of the amplifier-fault input is determined by bit 23 of Ixx24
and the polarity of the amplifier-enable output must be determined with the hardware interface.