Reference Manual

PMAC 2 Software Reference
PMAC I-Variable Specification 119
PMAC2 supports interface to serial analog-to-digital converters of many resolutions
through its “DSPGATE1” ASIC. The data is received in 18-bit shift registers in the ASIC,
which are read as the high end of a 24-bit word, with the number “left-justified” to the
most significant bit.
Ix84 specifies a 24-bit mask word that is combined with the feedback word through a
logical AND operation to produce the value that is used in the current loop equations.
There should be a 1 in every bit that is used, and a 0 in every bit that is not. Since the data
is left justified, Ix84 should start with 1s and end with 0s. Usually Ix84 is represented as a
hexadecimal number, with 4 bits per digit, and a total of six digits
Some direct-PWM amplifiers will transmit status and fault information on the end of the
serial data stream for the ADC, and it is important to mask out these values from the
current loop equations.
Example
For a 10-bit ADC: Ix84=$FFC000
For a 12-bit ADC: Ix84=$FFF000
For a 16-bit ADC: Ix84=$FFFF00
Further Motor I-Variables
Ix85 Motor x Backlash Take-up Rate
Range
0 .. 8,388,607
Units
(1/16 Counts) / Background Cycle
Default
0
Remarks
Ix85 determines how fast backlash is “taken up” on direction reversal. The size of the
backlash is determined by Ix86, and possibly the backlash compensation table for the
motor. PMAC will “take up” the backlash at the Ix85 rate whenever the commanded or
Master Handwheel position for the motor reverses more than 4 encoder counts. If Ix85 is
zero, backlash is effectively disabled. Ix85 is usually set as high as possible without
creating dynamic problems.
Variable I99, Backlash Hysteresis, determines the amount of reversal in desired position
that is required before backlash will start to be introduced or removed.
See Also
I-variables I99, Ix64, Ix65, Ix68, Ix86
On-line commands DEFINE BLCOMP, DELETE BLCOMP
Backlash Compensation (Setting Up a Motor)
Ix86 Motor x Backlash Size
Range
-8,388,608 .. 8,388,607
Units
1/16 Count
Default
0
Remarks
Ix86 allows PMAC to compensate for backlash in the motor’s coupling by adding or
subtracting (depending on the new direction) the amount specified in the parameter to the
commanded position on direction reversals (this offset will not appear when position is
queried or displayed). A value of zero means no backlash. Negative values of Ix86 can be
useful if the motor is slaved to another motor that has more backlash than the slave.
The rate at which this backlash is added or subtracted (taken up) is determined by Ix85.
Variable I99, Backlash Hysteresis, determines the amount of reversal in desired position
that is required before backlash will start to be introduced or removed.