Hello Everybody,
after noticing some bad noises on a machine I noticed that when I
command an output of -10.0V on an stg2 card that it actually outputs +10V.
To debug and reproduce I did this:
setp stg.2.dac-value -10
or
setp stg.2.dac-value -9.999
measured approx. +10V with a voltmeter, not ok
setp stg.2.dac-value -9.99
measured approx. -9.96V with a voltmeter, ok
Such large values should not usually happen if you use the dac output
for a servo amp because then you've run into saturation, but if you use
the output for something else, like spindle velocity control+ direction,
then it really does.
The relevant code is how the ncounts variable gets
calculated in hal_stg.c:
ncounts = (short) ((-10.0 - volts) / 20.0 * 0x1FFF);
The relevant stg documentation is on p. 30 of the stg2 manual. Values
written to the register are inverted before arriving at the dac.
0x0000 => -10V
0x1000 => 0V
0x1FFF => +10V
Changing the calculation to:
ncounts = (short) ((((-10.0 - volts) * 0x1FFF) / 20.0) - 1 );
solves the problem. Check with the attached test program. Notice the
0xFFFF values for -10V after the inverting is done in the old calc.
Current Emc2 calculation: Values written to register are: -10V: 0x0000,
-9,999V: 0x0000, -9,99V: 0xFFFC, 0V: 0xF001, +10V: 0xE001
Current Emc2 calculation: Values arriving at DAC (inverted) are: -10V:
0xFFFF, -9,999V: 0xFFFF, -9,99V: 0x0003, 0V: 0x0FFE, +10V: 0x1FFE
Mod. Emc2 calculation: Values written to register are: -10V: 0xFFFF,
-9,999V: 0xFFFF, -9,99V: 0xFFFB, 0V: 0xF000, +10V: 0xE000
Mod. Emc2 calculation: Values arriving at DAC are: -10V: 0x0000,
-9,999V: 0x0000, -9,99V: 0x0004, 0V: 0x0FFF, +10V: 0x1FFF
I also checked this fix 5 mins ago on the real machine - works now.
BR
Max.
#include <stdio.h>
short emc2_calc( double lvolts )
{
short retval ;
retval = (short) ((-10.0 - lvolts) / 20.0 * 0x1FFF);
return retval;
}
short emc2_calc_mod( double lvolts )
{
short retval ;
retval = (short) ((((-10.0 - lvolts) * 0x1FFF) / 20.0) - 1 );
return retval;
}
int main( int argc, char **argv )
{
short n0, n1, n2, n3, n4;
short m0, m1, m2, m3, m4;
n0 = emc2_calc( -10.0L );
n1 = emc2_calc( -9.999L );
n2 = emc2_calc( -9.99L );
n3 = emc2_calc( 0.0L );
n4 = emc2_calc( +10.0L );
printf( "Current Emc2 calculation: Values written to register are: -10V: 0x%04hX, -9,999V: 0x%04hX, -9,99V: 0x%04hX, 0V: 0x%04hX, +10V: 0x%04hX\n", n0, n1, n2, n3, n4 );
printf( "Current Emc2 calculation: Values arriving at DAC (inverted) are: -10V: 0x%04hX, -9,999V: 0x%04hX, -9,99V: 0x%04hX, 0V: 0x%04hX, +10V: 0x%04hX\n", ~n0, ~n1, ~n2, ~n3, ~n4 );
m0 = emc2_calc_mod( -10.0L );
m1 = emc2_calc_mod( -9.999L );
m2 = emc2_calc_mod( -9.99L );
m3 = emc2_calc_mod( 0.0L );
m4 = emc2_calc_mod( +10.0L );
printf( "Mod. Emc2 calculation: Values written to register are: -10V: 0x%04hX, -9,999V: 0x%04hX, -9,99V: 0x%04hX, 0V: 0x%04hX, +10V: 0x%04hX\n", m0, m1, m2, m3, m4 );
printf( "Mod. Emc2 calculation: Values arriving at DAC are: -10V: 0x%04hX, -9,999V: 0x%04hX, -9,99V: 0x%04hX, 0V: 0x%04hX, +10V: 0x%04hX\n", ~m0, ~m1, ~m2, ~m3, ~m4 );
return 0;
}
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