Reference Manual

Turbo PMAC/PMAC2 Software Reference
Turbo PMAC Global I-Variables 108
Note:
The units of this parameter are 1/16 of a count, so the value should be 16 times the
number of counts between the trigger position and the home zero position.
Example:
To change the motor zero position to 500 counts in the negative direction from the home trigger position,
set Ixx26 to -500 * 16 = -8000.
Ixx27 Motor xx Position Rollover Range
Range: -2
35
- +2
35
Units: counts
Default: 0
Ixx27 permits either of two position rollover modes on a Turbo PMAC rotary axis assigned to Motor xx
by telling Turbo PMAC how many encoder counts are in one revolution of the rotary axis. This lets
Turbo PMAC handle rollover properly. If Ixx27 is set to the default value of 0, no rollover mode is
active, and the axis is treated as a linear axis.
If Ixx27 is greater than zero, and Motor xx is assigned to a rotary axis (A, B, or C), the standard rollover
mode is active. With standard rollover active, for a programmed axis move in absolute (ABS) mode, the
motor will take the shortest path around the circular range defined by Ixx27 to get to the destination point.
No absolute-mode move will be longer than half of a revolution (Ixx27/2) with standard rollover.
If Ixx27 is set to a negative number, an alternate rollover mode for the rotary axis assigned to the motor is
activated that uses the sign of the commanded destination in absolute mode to specify the direction of
motion to that destination. In this mode, all moves are less than one revolution (with the size of the
revolution specified by the magnitude of Ixx27), but can be greater than one-half revolution. This mode
also does not affect the action of incremental-mode moves.
The sign of the commanded absolute destination in this mode is also part of the destination value.
Therefore, a command of A-90 in this mode is a command to go to -90 degrees (= +270 degrees) in the
negative direction. For commands to move in the positive direction, the + sign is not required, but it is
permitted (e.g. to command a move to 90 degrees in the positive direction, either A90 or A+90 can be
used).
PMAC cannot store the difference between a +0 and a –0 destination command, so a command with a
tiny non-zero magnitude for the end position must be used (e.g. A+0.0000001 and A-0.0000001).
This increment can be small enough not to have any effect on the final destination.
If the distance of the move commanded in alternate rollover mode is less than the size of the in-position
band defined for the motor with Ixx28, no move will be executed. This means that the minimum distance
for a move in this mode is Ixx28, and the maximum distance is 360 degrees minus Ixx28.
If using commands from a similar mode in which only the magnitude, and not the sign, of the value
specifies the destination position, then the destination values for negative-direction moves must be
modified so that the magnitude is 360 degrees minus the magnitude in the other mode. For example, if
the command were C-120, specifying a move to (+)120 degrees in the negative direction, the command
would have to be modified for PMAC to C-240, which specifies a move to -240 degrees (= +120 degrees)
in the negative direction. Commands for positive-direction moves do not have to be modified.
Axis moves in incremental (INC) mode are not affected by either rollover mode. Rollover should not be
attempted for axes other than A, B, or C. Jog moves are not affected by rollover. Reported motor
position is not affected by rollover. (To obtain motor position information rolled over to within one
motor revolution, use the modulo (remainder) operator, either in PMAC or in the host computer: e.g.
P4=(M462/(I408*32))%I427).