Publication 1734-UM006B-EN-P - August 2005
Input and Output Data 3-7
Scalar (Configuration Word 7)
This bytel scales the Z signal in the period/rate [5] configuration. If the
filter is applied, then the filtered Z is scaled. Only one bit of the scalar
should be set. Selecting a scalar will cause accumulated counts to be
adjusted accordingly (selecting a scalar of 128 will increase the
accumulated count by 128 after 128 Z pulses have been received). We
highly recommend that anytime Z is scaled (divide by 2, 4, 8), the Z
input should be filtered, otherwise, noise could cause erroneous
frequency readings.
Scalar Selection
Rollover (Configuration Word 8)
This long word sets the number of counts the counter will
accumulate before rolling over. For example, a value of 1000 will
produce a count sequence of: 998, 999, 0, 1, 2… while incrementing
or 2, 1, 0, 999, 998… while decrementing. Rollover is a 32 bit number
with a useable range of 1 ≤ value ≤ 0x01000000 (16,777,216). In count
[0], x1 encoder [1], x2 encoder [2] and x4 encoder [4] configurations, it
should be specified to some non-zero value; and in period/rate [5],
and rate measurement [7] configurations is a ‘don’t care’.
Preset (Configuration Word 9)
This long word sets the preset value the counter will be loaded with,
when a Counter Preset, CP, command is issued. Preset is a 32 bit
number with a range of 0 ≤ value ≤ 0x00FFFFFF (16,777,215).
07 06 05 04 03 02 01 00
Scalar
1
00000001Z - F
min
= 0.149Hz
00000 010Z/2 - F
min
= 0.298Hz
00000100Z/4 - F
min
= 0.596Hz
00001000Z/8 - F
min
= 1.192Hz
00010000Z/16 - F
min
= 2.384Hz
0010 0000Z/32 - F
min
= 4.768Hz
01000000Z/64 - F
min
= 9.537Hz
10000000Z/128 - F
min
= 19.073Hz
1Where F
min
indicates the frequency at which the zero frequency detect is asserted
due to counter overflow.
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