Reference Manual

PMAC 2 Software Reference
PMAC I-Variable Specification 111
Absolute motor position read: If Ix10 is set to 0, the position reference for a motor comes
from a homing search move. If Ix10 is greater than 0, the position reference comes from
reading an absolute position sensor at the address and with the format specified by Ix10. In this
case, Ix80 bit 2 specifies whether or not this read is done automatically at power-up/reset.
If the absolute position read is not done automatically at power-up/reset, the motor position will
be set to 0 at this time. This does not prevent full operation of the motor. The $* command
must be used later to read the sensor and establish absolute position. Even if the absolute
position is read automatically at power-up/reset, it may be read again later with the $*
command.
See Also
Power-Up Phasing Search (Setting Up PMAC Commutation)
On-line commands $, $$, $*, $$$
I-Variables Ix01, Ix73, Ix74, Ix78, Ix81
Ix81 Motor x Power-Up Phase Position Address
Range
$000000 .. $FFFFFF
Units
Extended PMAC Addresses
Default
0
Remarks
Ix81 tells PMAC what address to read for absolute power-on phase-position information
for Motor x, and how to read it, if such information is present. This can be a different
address from that of the ongoing phase position information, which is specified by Ix83.
Ix81 is set to zero if no special power-on phase position reading is desired, as is the case
for an incremental encoder.
If Ix81 is set to zero, a power-on phasing search routine is required for synchronous fixed-
field brushless motors (permanent magnet, and switched reluctance); those that have a slip
gain (Ix78) of zero. PMAC’s automatic phasing search routines based on Ix73 and Ix74
can be used, or a custom power-on PLC routine can be written.
Note:
Ix81 is used for PMAC’s commutation algorithms alone, to locate
position within one electrical cycle of the motor. It is not used for
any servo loop position information, even for power-up. Ix10 is
used for that purpose.
Ix81 consists of two parts. The low 16 bits contain the address of the register containing
the power-on position information, either a PMAC memory-I/O address, or an address on
the multiplexer (“thumbwheel”) port. The high 8 bits specify how to read the information
at this address.
Note:
It is easier to specify this parameter in hexadecimal form ($ prefix).
If I9 is set to 2 or 3, the value of this variable will be reported back
to the host in hexadecimal form.