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Parameter Dictionary
There are several drive parameters which are used to define filters. These filters are implemented as generic biquadratic filter structures.
Filters of this type implement the following formula to transform the input parameter x(n) at time n to an output parameter y(n):
y(n) = b0·x(n) + b1·x(n-1) + b2·x(n-2) + a1·y(n-1) + a2·y(n-2)
The values a1, a2, b0, b1, b2 are constants known as filter coefficients. They define the type of filter being implemented.
The values passed to these drive filter parameters are used to define the filter coefficients. The formatting of these parameters varies
depending on the drive family being interfaced to.
All first generation Copley drives use 16-bit integer math to implement their filters internally. Filter coefficients are given as 16-bit signed
integer values. To increase the resolution of these coefficients, an additional unsigned scaling coefficient (k) is also specified. The actual
filter formula used within these drives is as follows:
y(n) = K · (b0·x(n) + b1·x(n-1) + b2·x(n-2) + a1·y(n-1) + a2·y(n-2)) / 32768 / 4096
To set the filter coefficients on drives of this category, 9 words of parameter data are passed. The first three words of data are informational
parameters which are used by the CME software to describe the filter. If the upper 3 bits of the first word are all set then the filter will be
disabled. Other than that, the first three words of data are not used in any way by the firmware. These three words are reserved for CME
use.
Word
Description
1
Filter info. Set to 0xFFFF to disable the filter. Otherwise, reserved for CME use.
2
Filter info. Reserved for CME use.
3
Filter info. Reserved for CME use.
4
b2 coefficient.
5
b1 coefficient.
6
b0 coefficient.
7
a2 coefficient.
8
a1 coefficient.
9
K scaler.
For the plus family of drives (Xenus+, AEM, etc), a new format is used to describe the biquad filter coefficients. These drives include the
ability to design the filters in firmware using the Cephes filter design library.
Filters on this family of drives are calculated internally using 32-bit IEEE floating point coefficients. The format of the parameter information
passed when setting filter parameters on these drives consists of an array of up to fourteen 16-bit words. The first 4 words describe the filter,
Copley Controls Page 74