PMAC/PMAC2 V1.17C Addendum No shifting action is performed. Any operations such as 1/T interpolation should have been done on the data already, so the source register for this filter is typically the result register of the previous operation. Method/Address Word: The first setup line of an exponential filter entry contains a ‘D’ in the first hex digit (bits 20 – 23), a ‘0’ in the second hex digit, and the address of the source X-register in the third through sixth hex digits (bits 0 – 15).
If it is desired to execute an exponential filter on the contents of a Y-register, the contents of the Y-register must first be copied to an X-register in the conversion table with a “parallel” entry ($2) higher in the table. The source addresses for exponential filter entries are almost always from the conversion table itself (X:$0720 – X:$073C). For example, to perform an exponential filter on the result of the fourth line of the table, the first setup line of the filter entry would be $D00723. Maximum Change Word: The second setup line of an exponential filter entry contains the value “max change” that limits how much the entry can change in one servo cycle.
The units of this entry are whatever the units of the input register are, typically 1/32 of a count. For example, to limit the change in one servo cycle to 64 counts with an input register in units of 1/32 count, this third line would be 64*32 = 2048. Filter Gain Word: The third setup line of an exponential filter entry contains the filter gain value K , which sets a filter time constant T f of (2 23 / K )-1 servo cycles. Therefore, the gain value K can be set as 2 23 /( T f +1). For example, to set a filter time constant of 7 servo cycles, the filter gain word would be 8,388,608/(7+1) = 1,048,576. Result Word:
The output value of the exponential filter is placed in the X register of the third line of the conversion table entry. An operation that uses this value should address this third register; for example Ix05 for position following, or the source address for a time-base conversion-table entry (to keep position lock in time base, this filter must be executed before the time-base differentiation, not afterward). Tracking Filter ($D8xxxx) For the tracking filter, the equation of the filter every servo cycle n is:
If [In(n) - In(n-1)] > Max_change, In(n) = In(n-1) + Max_change If [In(n) - In(n-1)] Err(n) = In(n) – Out(n-1) Temp1 = (Kp/2 23 ) * Err(n) Int(n) = Int(n-1) + (Ki/2 23 ) * Err(n) Out(n) = Out(n-1) + Temp1 + Int(n) In , Out , K p and K i are all signed 24-bit numbers (range -8,388,608 to 8,388,607). The difference [In(n)-Out(n-1)] is truncated to 24 bits to handle rollover properly. The time constant of the filter, in servo cycles, is (2 23 /K p )-1. The lower the value of K p , the longer the time constant. No shifting action is performed.
Any operations such as 1/T interpolation should have been done on the data already, so the source register for this filter is typically the result register of the previous operation. 20 V1.17C Firmware Version