Delta Tau GEO BRICK LV User Manual
Turbo PMAC User Manual
Setting Up Feedback and Master Position Sensors
59
For details of setting up the encoder conversion table to process sinusoidal encoders, consult the section
Setting up the Encoder Conversion Table section in this manual and the specification for variables I8000
– I8191 in the Software Reference Manual.
Setting up the Encoder Conversion Table section in this manual and the specification for variables I8000
– I8191 in the Software Reference Manual.
Encoder Interpolation: Analog SIN/COS Encoders
+
-
SIN / COS
Signals
A
B
A
B
n-bit
A/D
n-bit
A/D
n
n
n-1, n bits
0
2
n
- 1
0
2
n
- 1
Differential
Amplifier
+
-
Analog
Photo
Current
Encoder
Controller
Flash
A/D
Converters
Arctan
Look-Up
Table
SIN / COS
Numbers
Angle
Number
Conversion Table Processing Setup – MACRO Station Interface
Sinusoidal encoders wired into a high-resolution (x4096) Acc-51x interpolator connected to a MACRO
Station CPU are processed in the MACRO Station CPU’s conversion table by a hi-res interpolator entry
(method digit $F), in which the fractional-count data is computed mathematically from the readings of the
sine and cosine A/D converters. The least significant bit (LSB) of the result represents 1/4096 of an
encoder line. This data is then passed over the MACRO ring to the Turbo PMAC, where it is processed
as unshifted parallel data (method digit $2).
Station CPU are processed in the MACRO Station CPU’s conversion table by a hi-res interpolator entry
(method digit $F), in which the fractional-count data is computed mathematically from the readings of the
sine and cosine A/D converters. The least significant bit (LSB) of the result represents 1/4096 of an
encoder line. This data is then passed over the MACRO ring to the Turbo PMAC, where it is processed
as unshifted parallel data (method digit $2).
Sinusoidal encoders wired into a “low-resolution (x128/x256) interpolator connected to a MACRO
Station CPU are processed in the MACRO Station CPU’s conversion table by a parallel extension of
incremental encoder entry (method digit $C), in which the fractional-count data has been computed
externally in the interpolator’s look-up table and is just appended to the whole count data by the
conversion table. The LSB of the result represents 1/128 or 1/256 of an encoder line, depending on the
setting of the resolution jumper on the interpolator. This data is then passed over the MACRO ring to the
Turbo PMAC, where it is processed as unshifted parallel data (method digit $2).
Station CPU are processed in the MACRO Station CPU’s conversion table by a parallel extension of
incremental encoder entry (method digit $C), in which the fractional-count data has been computed
externally in the interpolator’s look-up table and is just appended to the whole count data by the
conversion table. The LSB of the result represents 1/128 or 1/256 of an encoder line, depending on the
setting of the resolution jumper on the interpolator. This data is then passed over the MACRO ring to the
Turbo PMAC, where it is processed as unshifted parallel data (method digit $2).
For details of setting up the encoder conversion table to process sinusoidal encoders, consult the MACRO
Station manuals and the Setting up the Encoder Conversion Table section in this manual and the
specification for variables I8000 – I8191 in the Software Reference Manual.
Station manuals and the Setting up the Encoder Conversion Table section in this manual and the
specification for variables I8000 – I8191 in the Software Reference Manual.
Scaling the Feedback Units
Turbo PMAC automatically considers the data it reads for the servo with Ixx03, Ixx04, and Ixx05 to be in
units of 1/32 of a count (i.e. to have 5 bits of fractional count resolution). With data processed in the
conversion table from a sinusoidal-encoder interpolator, be very careful to understand what a count is.
units of 1/32 of a count (i.e. to have 5 bits of fractional count resolution). With data processed in the
conversion table from a sinusoidal-encoder interpolator, be very careful to understand what a count is.