Delta Tau GEO BRICK LV Manuel D’Utilisation

Turbo PMAC uses a two-step process to work with its feedback and master position information for the 
servo algorithm, to provide maximum power and flexibility.  (Note that the commutation algorithms 
generally use raw feedback registers unprocessed by the conversion table.)  For most Turbo PMAC users 
with quadrature encoder feedback, this process can be virtually transparent, with no need to worry about 
the details.  However, some users will need to understand this conversion process in some detail to make 
the changes necessary to use other types of feedback, to optimize their system, or to perform special 
functions.  This section is for those users. 

The first stage in the position processing uses the hardware registers such as encoder counters with 
associated timers, A/D registers, or accessory cards for parallel input.  These work continually without 
direct software intervention (although they can be configured through software) with data typically 
latched on the servo interrupt.  This stage is covered in the Hardware Reference manual for the particular 
device and the Setting up Feedback section of this manual.  Beyond this point, the process is software-
controlled.   

Most controllers use the raw data in the hardware registers directly for feedback or master position data.  
However, Turbo PMAC has an intermediate step using a software structure called the Encoder 
Conversion Table to pre-process the information in the latched registers.  This table tells PMAC what 
registers to process, and how to process them; it also holds the intermediate processed data. 

Ix03: Position Loop Feedback Address
Ix04: Velocity Loop Feedback Address
Ix05: Master Position Address
Ix93: Time Base Source Address

To Servo
Algorithms

Address

Data

Address

Data

Conversion Instructions:

Process & Address

Processed

Feedback Data

RAM

Raw

Feedback

Data

Encoder Counters

& Timers, Latches, ADC's

Servo Address

I-Variables

Feedback

Data Signals

 

This pre-processing step is necessary, or at least advantageous for several reasons: 

• 

There are several pieces of raw data that need to be combined into one resulting position number, as 
with the counter and timers for “1/T” encoder interpolation. 

• 

There is some checking for special conditions (such as rollover or sudden changes indicative of noise, 
which needs to be done to ensure robust data. 

• 

Mathematical processing of the raw data, such as addition, subtraction, differentiation, or integration, 
needs to be done to get the resulting value. 

• 

The raw data just needs to be transferred and shifted for the servo algorithm to use. 

While the primary purpose of the table is to produce processed (converted) values for feedback and 
master position data for the servo algorithms to use, other uses are possible.  The table’s guaranteed 
execution at the beginning of each servo cycle, and its many tools for processing data, permit other uses 
as well.