On Wed, Sep 15, 2010 at 12:42:55PM -0500, Jon Elson wrote:
> The PPMC
> driver takes a +/- 1.0 value and multiplies it by 10 to give a +/- 10 V
> output range.
Are you sure? I was looking at the pwmgen code earlier instead of the
dac code (not sure how these differ) and I *think* pwmgen full scale
value at the hal input pin is +-1 and dac full scale value at the hal
input pin is +-10.
I think this means the scale I suggested is off by a factor of 10
(should have been 0.889 instead of 8.89). Here's the relevant code
from the ppmc driver:
volts = *(pg->value) / pg->scale;
dc = (long) (((volts / 10.0) * 0x7FFF)+0x8000);
Confusingly, I think we have
PPMC:
output in volts = value / scale
Hostmot2:
output in volts = 10 * (value / scale)
STG:
output in volts = (value - offset) * scale
VTI:
output in volts = (value - offset) * scale
Motenc:
output in volts = (value - offset) * scale
(yay, I guess a few of them match)
HAL Canonical analog output:
output in volts = scale * value + offset
or maybe the documentation means this (not sure):
output in volts = scale * (value + offset)
(HAL docs are from the time machine):
http://www.linuxcnc.org/docs/2.1/html/hal/general_ref/index.html
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