Reference Manual

PMAC 2 Software Reference
378 PMAC Saved Setup Registers
also be read. The selected bytes of these three registers are combined into a single 24-bit value, with the
selected byte of the first register forming the least significant byte of this value. The mask word of the
second setup line (see below) then operates on this combined value as if it had come from a single 24-bit
word.
Examples of this byte-wide conversion with the ACC-14P are shown below.
Mask Word: The second setup line is a 24-bit mask word that indicates which bits of the 24-bit word-wide
source register, or of the 24-bit value combined from 3 byte-wide reads, are to be used. Each bit that is to
be used takes a 1 in the mask word; each bit that is not to be used takes a 0 in the mask word. The mask
word is combined with the contents of the source register or combined value with a bit-by-bit AND
operation before the data is processed further. A correct 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 Feedback: When receiving position data over the MACRO ring with the “Type 1” protocol used
in Delta Tau and most other MACRO devices, the position feedback appears in the 24-bit Register 0 for
the “servo node”. Servo 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). This position data has
usually already been processed in the encoder conversion table of the remote MACRO Station 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
Node 1
st
Setup
Line
Node 1
st
Setup
Line
Node 1
st
Setup
Line
Node 1
st
Setup
Line
0 $28C0A0 4 $28C0A8 8 $28C0B0 12 $28C0B8
1 $28C0A4 5 $28C0AC 9 $28C0B4 13 $28C0BC
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
Node 1
st
Setup
Line
Node 1
st
Setup
Line
Node 1
st
Setup
Line
Node 1
st
Setup
Line
2 $68C0A0 6 $68C0A8 10 $68C0B0 14 $68C0B8
3 $68C0A4 7 $68C0AC 11 $68C0B4 15 $68C0BC
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