PMAC/PMAC2 V1.17C Addendum 12-bit section should be treated as a signed 12-bit value (so if the most significant of the 12 bits is a 1, the bias value is negative). Each 12-bit bias-correction term should contain the value opposite that which the high 12 bits of the matching A/D converter report when they should ideally report zero. In action, the bias term will be added to the high 12 bits of the corresponding ADC reading before subsequent calculations are done. For example, if the bias-correction word were set to $004FFA, the sine bias correction would be +4 LSBs of a 12-bit ADC, and the cosine bias correction would be -6 LSBs ($FFA = -6) of a 12- bit ADC.
In use, 4 12-bit LSBs would be added to the sine reading, and 6 12-bit LSBs would be subtracted from the cosine reading each cycle before further processing. In most cases, the bias-correction word will be determined automatically by an analog “diagnostic” entry in the conversion table. The result of that diagnostic entry, containing both bias corrections, can simply be copied into this setup word. R ESULT W ORD : T HE OUTPUT VALUE OF THE HIGH - RESOLUTION SINUSOIDAL - ENCODER CONVERSION IN THE G EO PMAC IS PLACED IN THE 24- BIT X- REGISTER OF THE THIRD LINE OF THE CONVERSION TABLE ENTRY .
B IT 0 OF THE RESULT CONTAINS THE LSB OF THE CONVERSION , REPRESENTING 1/4096 OF A LINE OF THE ENCODER . S INCE PMAC SOFTWARE CONSIDERS THE CONTENTS OF B IT 5 TO BE A “ COUNT ” FOR SCALING PURPOSES WHEN USED FOR SERVO FEEDBACK OR MASTER DATA , BIT 0 WILL BE CONSIDERED 1/32 OF A COUNT . T HIS MEANS THAT PMAC SOFTWARE WILL SCALE THE DATA AS 128 “ SOFTWARE COUNTS ” PER LINE OF THE ENCODER .
High-Resolution Interpolation Diagnostic Entry ($Fxxxxx, bit 19 = 1) [Geo PMAC only] I F BIT 19 OF THE FIRST SETUP LINE OF A G EO PMAC “ INTERPOLATION ” ENTRY IS 1, TO SPECIFY AN ENTRY THAT PRODUCES EITHER VECTOR MAGNITUDE OR ANALOG - INPUT BIAS TERMS FOR THE SINE AND COSINE INPUTS OF A SINUSOIDAL ENCODER OR RESOLVER , THIS IS A FIVE - LINE ENTRY . T HESE RESULT VALUES CAN BE USED TO VERIFY PROPER SETUP AND INTERFACE OF THE ENCODER OR RESOLVER AND TO OPTIMIZE THE ACCURACY OF THE CONVERSION DURING INITIAL SETUP , AND / OR TO CHECK FOR LOSS OF THE ENCODER OR RESOLVER DURING THE ACTUAL APPLICATION .
B IT 16 OF THE FIRST SETUP LINE DETERMINES WHETHER THE RESULT PRODUCED IS THE SUM OF THE SQUARES OF THE TWO ANALOG INPUTS ( BIT 16 = 0) OR THE BIAS TERMS FOR THE ANALOG INPUTS ( BIT 16 = 1). Method/Address Setup Word : The first setup line of the five-line entry contains $F in the first hex digit, $8 in the second hex digit (bit 19 = 1) to produce a sum-of-squares result or $9 in the second digit (bit 19 = 1, bit 16 =1) to produce a bias correction term, and the address of the first of the two A/D converters in the low 16 bits (the last four hex digits). The second A/D converter will be read at the next higher address.
In the Geo PMAC, the first A/D converter for Channel 1 is at address $FF00, and the first A/D converter for Channel 2 is at address $FF20, so the first setup line is set to $F8FF00 or $F8FF20 to produce a sum-of-squares result, or to $F9FF00 or $F9FF20 to produce a bias-correction result. When set up to determine the bias term, if bit 17 is set to 0, making the second hex digit $9 (as the above instructions say), the minimum and maximum values for the sine and cosine readings that are used to determine the appropriate bias values are set to 0.
As soon as the Geo PMAC starts accumulating minimum and maximum values (the next servo cycle), it will set bit 17 to 1, making the second hex digit to $B. If you want to start a new test, for example after a circuit adjustment, you must set bit 17 to 0 again by making the second hex digit $9. 24 V1.17C Firmware Version