PMAC/PMAC2 V1.17C A DDENDUM J UL -2005 mask word is necessary to ensure that all bits of the source to be used are used, that no bits that are not to be used are used, and to handle rollover of the source data properly. For example, a mask word of $000FFF causes the low 12 bits of the source register to be used, $07FFFF causes the low 19 bits to be used, and $FFFFFF causes all 24 bits to be used. Maximum Change Word: If the method character for a parallel read is $3 or $7, specifying “filtered” parallel read, there is a third setup line for the entry.
This third line contains the maximum change in the source data in a single cycle that will be reflected in the processed result, expressed in LSBs per servo cycle. The filtering that this creates provides an important protection against noise and misreading of data. This number is effectively a velocity value, and should be set slightly greater than the maximum true velocity ever expected. Common Parallel Data Sources : Any register can be read as a parallel data source, but the most common sources are MACRO feedback registers, MLDT timer registers, ACC-14D/V latched input registers, and ACC-14P byte-wide latched input registers. Each of these is covered below. MACRO F EEDBACK :
W HEN RECEIVING POSITION DATA OVER THE MACRO RING WITH THE “T YPE 1” PROTOCOL USED IN D ELTA T AU AND MOST OTHER MACRO DEVICES , THE POSITION FEEDBACK APPEARS IN THE 24- BIT R EGISTER 0 FOR THE “ SERVO NODE ”. S ERVO NODES ARE MAPPED INTO Y- REGISTERS IN PMAC2, AND THE MACRO PROTOCOL HAS ITS OWN ERROR DETECTION , SO TYPICALLY METHOD $2 IS USED (Y- REGISTER , NO FILTERING ). T HIS POSITION DATA HAS USUALLY ALREADY BEEN PROCESSED IN THE ENCODER CONVERSION TABLE OF THE REMOTE MACRO S TATION AND COMES BACK WITH FIVE BITS OF FRACTIONAL INFORMATION , SO IT DOES NOT NEED TO BE SHIFTED IN THE CONVERSION TABLE , MAKING THE SECOND DIGIT $8.
MACRO Type 1 Position Feedback Sometimes a MACRO I/O node is used to bring back additional position data. I/O nodes are mapped into X-registers in PMAC2, so typically method $6 is used (X-register, no filtering). This position data also has typically been processed in the remote MACRO Station, so the second digit is $8 for no shifting here. MACRO I/O Node Register 0 as Alternate Position Feedback MLDT Feedback : PMAC2 Servo ICs have the ability to interface directly to magnetostrictive linear displacement transducers (MLDTs), outputting the excitation pulse, receiving the echo pulse, and measuring the time between the two. This time is directly proportional to the distance.
For this feedback the “time between last two counts” register is used like an absolute encoder. The following table shows the first line of the parallel feedback entry for each channel’s timer register: V1.17C Firmware Version 17 Node 1st Setup Line Node 1st Setup Line Node 1st Setup Line Node 1st Setup Line 0 $28C0A0 4 $28C0A8 8 $28C0B0 12 $28C0B8 1 $28C0A4 5 $28C0AC 9 $28C0B4 13 $28C0BC Node 1st Setup Line Node 1st Setup Line Node 1st Setup Line Node 1st Setup Line 2 $68C0A0 6 $68C0A8 10 $68C0B0 14 $68C0B8 3 $68C0A4 7 $68C0AC 11 $68C0B4 15 $68C0BC