Delta Tau GEO BRICK LV User Manual

 

 

3.  Compare output invert control bit: If this bit is set to 0, the off state is a low voltage out of the Servo 

IC, and the on state is a high voltage.  (Depending on the output driver circuitry, the actual output 
from the card may be inverted from this.)  If this bit is set to 1, the off state is a high voltage and the 
on state is a low voltage.  Note that this control bit can be used by itself to make the compare output a 
general-purpose digital output, or in some cases, a software-driven interrupt to the host computer. 
The single status bit is the position-compare flag, which shows the present state of the compare output 
logic (and if the output is enabled, of the physical output).  It is set to 1 if the compare output logic 
state is on, and to a 0 if the output logic state is off. 

There are no firmware functions for the automatic use of the position-compare circuitry.  Your application 
software must deal with the compare registers and control/status bits directly.  Usually, these are accessed 
with M-variables, and the file of suggested M-variables includes these definitions.  For the first channel of 
a Turbo PMAC (Servo IC 0 Channel 1), these definitions are: 

M101->X:$078001,0,24,S   

; 24-bit position counter register 

M103->X:$078003,0,24,S   

; 24-bit position compare register 

M111->X:$078000,11,1 

 

; Compare flag latch control 

M112->X:$078000,12,1 

 

; Compare output enable control 

M113->X:$078000,13,1 

 

; Compare output invert control 

M116->X:$078000,16,1 

 

; Compare logic status 

To preload a compare position, simply write a value to the compare register (e.g. M103=1250). 
Example: We have an array of 50 points in P1 through P50 that represent the distances from a starting 
position at which we want compare outputs.  Program code (running just a single time) that could start 
this process is: 

P100=1 

; Select first point of array 

P101=M101 

; Read and store starting position 

M103=P101+P(P100) 

; Write first relative position to compare 

M111=1 

; Set for latched output 

M112=1 

; Enable compare output 

Repeatedly executing program code (probably in a PLC 0 or PLCC 0) that could work through the array 
is: 

WHILE (P100<51) 

; Loop until 50 points completed 

  IF (M116=1) 

; Reached last compare position? 

    P100=P100+1 

; Select next point 

    M103=P101+P(P100) 

; Write next relative position to compare 

    M111=0 

; Clear output by making transparent 

    M111=1 

; Set for latched output again 

Each encoder counter in PMAC2-style Servo IC has a position-compare function.  Furthermore, the first 
encoder counter (Channel 1) in each Servo IC can use the position-compare circuitry from any of the 
other channels on the ASIC, so it can utilize up to four independent compare circuits. 

On the Turbo PMAC2-PC and the Turbo PMAC2-PCI, the compare outputs for Channel 1 and Channel 5 
(if present) also can be used to interrupt the host computer over the backplane bus.  Note that if the dual-
ported RAM ASCII communications interrupt function is enabled (I56=1 and I58=1), the compare output 
for the board’s Channel 1 is used for this interrupt, and so cannot be used for true position compare 
functions.