Delta Tau GEO BRICK LV Manuel D’Utilisation
Turbo PMAC User Manual
Motor Compensation Tables and Constants
139
Final Result Format
In general, the 24-bit final result is structured as 19 bits of integer (bits 5 – 23) and five bits of fraction
(bits 0 – 4). The integer value represents whole number of least significant bits (LSBs) of a counter
(counts), a latched register or an analog-to-digital converter. In other words, the LSB of the main source
register is placed in bit 5 of the result register, a 5-bit shift. The fractional component represents a
measured or estimated value of finer resolution (which could always be zero in some methods); with 5
bits of fractional data, the result will have units of 1/32 of a count. Note that several methods yield a
measurement resolution that is finer than what the software considers a count.
(bits 0 – 4). The integer value represents whole number of least significant bits (LSBs) of a counter
(counts), a latched register or an analog-to-digital converter. In other words, the LSB of the main source
register is placed in bit 5 of the result register, a 5-bit shift. The fractional component represents a
measured or estimated value of finer resolution (which could always be zero in some methods); with 5
bits of fractional data, the result will have units of 1/32 of a count. Note that several methods yield a
measurement resolution that is finer than what the software considers a count.
However, this is not always so. It is possible in several conversion methods to specify an unshifted
conversion. When this is done, the LSB of the source data is placed in bit 0 of the result word, not the
usual bit 5. In the high-resolution analog encoder conversion, 10 bits of fraction are produced for each
count of the hardware encoder counter, so the result has units of 1/1024 of a quadrature count, or 1/4096
of an encoder line.
conversion. When this is done, the LSB of the source data is placed in bit 0 of the result word, not the
usual bit 5. In the high-resolution analog encoder conversion, 10 bits of fraction are produced for each
count of the hardware encoder counter, so the result has units of 1/1024 of a quadrature count, or 1/4096
of an encoder line.
When the final result value of the table entry is used for feedback or master position data by a Turbo
PMAC servo loop, the servo algorithm software will always consider this value to have units of 1/32 of a
count – to have the bit representing one count or LSB located in bit 5 – even if the conversion did not
place it there. This can lead to a difference in scaling between a software count and a hardware count. If
an unshifted conversion is used, the software will consider the LSB of the source register to be 1/32 of a
count. If the high-resolution analog encoder conversion is used, the software will consider one hardware
count of the quadrature counter to be 32 software counts, yielding 128 counts per line of the analog
encoder.
PMAC servo loop, the servo algorithm software will always consider this value to have units of 1/32 of a
count – to have the bit representing one count or LSB located in bit 5 – even if the conversion did not
place it there. This can lead to a difference in scaling between a software count and a hardware count. If
an unshifted conversion is used, the software will consider the LSB of the source register to be 1/32 of a
count. If the high-resolution analog encoder conversion is used, the software will consider one hardware
count of the quadrature counter to be 32 software counts, yielding 128 counts per line of the analog
encoder.
Intermediate Results
If the entry in the conversion table is more than one line in length, the lines in the result column before the
final line hold intermediate results. Typically, these are for internal use only; if there is any utility for the
user, this is documented in the Software Reference Manual for the conversion method.
final line hold intermediate results. Typically, these are for internal use only; if there is any utility for the
user, this is documented in the Software Reference Manual for the conversion method.
Using the Results
Most often, the processed data in the conversion table is used for feedback or master data for the servo
algorithms through one of the four following I-variables:
algorithms through one of the four following I-variables:
•
Ixx03
Motor xx Position-Loop Feedback Address
•
Ixx04
Motor xx Velocity-Loop Feedback Address
•
Ixx05
Motor xx Master Position Address
•
Isx93
Coordinate System x Time Base Source Address
The value of each of these variables is the address of the register that will be read each servo cycle to get
the appropriate information for the servo algorithms. These variables always use the X-register at the
specified address (which is the result column of the table).
the appropriate information for the servo algorithms. These variables always use the X-register at the
specified address (which is the result column of the table).
There are two ways to specify the value of these variables, and therefore the address that they use. The
first is to specify the address directly, and usually as a hexadecimal number (with $ prefix). The second
way is to specify the address indirectly, by reference to the I-variable at that address, using the ‘@’ symbol
in front of that I-variable name. This permits you to use the result without having to look up the address.
first is to specify the address directly, and usually as a hexadecimal number (with $ prefix). The second
way is to specify the address indirectly, by reference to the I-variable at that address, using the ‘@’ symbol
in front of that I-variable name. This permits you to use the result without having to look up the address.
The following table shows the I-variables and the addresses for the first 16 lines of the table, the most
commonly used. A table showing these for all 192 lines of the table is given in the formal description of
these variables in the Software Reference manual.
commonly used. A table showing these for all 192 lines of the table is given in the formal description of
these variables in the Software Reference manual.