User's Manual

PMAC User Manual
72 Setting Up a Motor
Unfiltered Parallel Feedback
X-Words Y-words
1. Intermediate data: Sign-extended most
significant word
1. Source and process
Bits 0-15:
Address of source data
Y-word if $20 conversion
X-word if $60 conversion
Bits 16-23:
= $20 for Y-word source
= $60 for X-word source
2. Converted data:
Bits 0-4: Fractional Bits
Bits 5-23: Integer Bits
2. Bit-enable mask
Bit=1 to use corresponding bit from source
word
Bit=0 not to use corresponding bit from
source word
Filtered Parallel Data Conversion
X-Words Y-words
1. Intermediate data:
Raw data reading
1. Source and process
Bits 0-15:
Address of source data
Y-word if $30 conversion
X-word if $70 conversion
Bits 16-23:
= $30 for Y-word source
= $70 for X-word source
2. Intermediate data:
Sign-extended most-significant word
2. Bit-enable mask
Bit=1 to use corresponding bit from source
word
Bit=0 not to use corresponding bit from
source word
3. Converted data:
Bits 0-4: Fractional Bits
Bits 5-23: Integer Bits
3. Filter value: Maximum permitted change in
counts/servo cycle
Uses
This unshifted format is intended for high-speed, very high-resolution applications, typically with parallel
laser-interferometer feedback. With the normal shifted format, the PMAC internal velocity registers
saturate when the counts/sec * Ix08 exceed 256M (268,435,456). With the unshifted format, this limit is
32 times higher: 8G (8,589,934,592).
Using this unshifted format, be aware that PMAC will treat on LSBit of the feedback device as 1/32 of a
count, not as a full count. For example, if there is a sensor on motor 1 (X-axis) with 2.5 nanometer
resolution, to program the axis in millimeters, treat one count as 80 nm (2.5*32) and make the axis
definition #1->12500X (1,000,000 / 80).
The conversion table entry for this would consist of a source and process word $38FFC2 (unshifted
parallel conversion of Y:$FFC2), a mask word $00FF00 (to use only the middle eight bits of the 24-bit
word), and a filter word value of something like $000020 (maximum speed 32 counts per servo cycle).
Ix05 for any motor x to be slaved to this handwheel would be set to the address of the third line of this
entry in the table. For a 1:1 following ratio and a default Ix08 value of 96, Ix07 would be set to 12
instead of the usual 96, to reflect that fact that each count from this accessory appears eight times bigger
than normal.