Reference Manual
Turbo PMAC/PMAC2 Software Reference
Turbo PMAC Global I-Variables 239
Note:
The bit 19 mode switch has been set to 1 so that the data out of the previous phase
position register from the MACRO ring is not shifted. This changes the second
hex digit from 0 to 8. Type 1 MACRO feedback comes with fractional count
information in the low five bits, so it does not need to be shifted.
The second line of an entry for previous phase position feedback should be $018000 to specify the use of
24 bits ($018) starting at bit 0 ($000).
MLDT Feedback: PMAC2-style 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:
Entries for PMAC2-Style MLDT Timer Registers
Servo
IC #
Chan. 1
Chan. 2
Chan. 3
Chan. 4
Notes
0
$378000
$378008
$378010
$378018
First IC on board PMAC2, 3U stack
1
$378100
$378108
$378010
$378018
Second IC on board PMAC2, 3U stack
2
$378200
$378208
$378210
$378218
First Acc-24E2x, first IC on first Acc-24P/V2
3
$378300
$378308
$378310
$378318
Second Acc-24E2x, second IC on first Acc-24P/V2
4
$379200
$379208
$379210
$379218
Third Acc-24E2x, first IC on second Acc-24P/V2
5
$379300
$379308
$379310
$379318
Fourth Acc-24E2x, second IC on second Acc-24P/V2
6
$37A200
$37A208
$37A210
$37A218
Fifth Acc-24E2x, first IC on third Acc-24P/V2
7
$37A300
$37A308
$37A310
$37A318
Sixth Acc-24E2x, second IC on third Acc-24P/V2
8
$37B200
$37B208
$37B210
$37B218
Seventh Acc-24E2x, first IC on fourth Acc-24P/V2
9
$37B300
$37B308
$37B310
$37B318
Eighth Acc-24E2x, second IC on fourth Acc-24P/V2
The second line in an MLDT entry should be $013000 to specify the use of 19 bits ($013) starting at bit 0
($000).
The third line in an MLDT entry should contain a number slightly greater than the maximum velocity
ever expected, expressed as timer increments per servo cycle. An increment of the 120 MHz timer
represents about 0.024mm (0.0009 in) on a typical MLDT device. This value represents the maximum
change in position reading that will be passed through the conversion table in a single servo cycle, and it
provides an important protection against missing or spurious echo pulses.
Time-Base Entries ($4, $9, $A, $B): A time-base entry performs a scaled digital differentiation of the
value in the source register. It is most often used to perform electronic cam functions, slaving a motion
sequence to the frequency of a master encoder. There are two types of time-base entries: “untriggered”
and triggered. An untriggered time base does not provide a specific starting point in the master source
data. A triggered time base starts the differentiation upon receipt of a hardware trigger on the master
encoder’s channel, referenced to the position captured by that trigger. This can be used to create an
absolute synchronization between the master position and the slave trajectory.
Time-base entries are two-line entries. The first setup line (I-variable) contains the method digit and the
address of the source-data register. The second setup line (I-variable) contains the time-base scale factor.
The first result line contains the intermediate result value of the source data, saved for the next cycle to be
able to compute the differentiation. The second result line contains the final result, which is the
differentiated value. Most commonly this result is used as the time-base source for a coordinate system,
so Isx93 for the coordinate system points to this second line.
Untriggered Time Base ($4): In an untriggered time-base entry, the first setup line (I-variable) contains a
4 in the method digit (bits 20 – 23) and the address of the source register in bits 0 – 18. The source
register is usually the result register of an incremental encoder entry (e.g. 1/T) higher in the table
(addresses $3501 to $35C0). Refer to the table above, which lists the addresses of each line in the