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PROCEDURE II
System Sizing for Natural Binary Output (Special Clock Frequency)
Procedure I above is for 95% of all applications, and provides a scaled output with best possible
manufacturing lead time. For applications requiring a shorter update time or a non-standard reso-
lution, use the following procedure to determine an approximate crystal frequency, number of
circulations, and update time. Note that systems requiring a special clock frequency can add 2-4
weeks to manufacturing time and slight additional cost.
The crystal frequency versus circulations for a given resolution is approximated by the following
formula:
Take the following steps:
1. Divide the stroke length by the resolution. This number gives the minimum number of counts
required. Use Table 1A to determine how many bits are required to accommodate this number.
2. Use the above formula to determine the clock frequency, fc, assuming N=1 and D = 1.
3. If the calculated frequency is greater than 40 MHz, divide by N = 2, 4, 8, 16, 32, etc., until you
find a value for N which determines an fc between 11 and 40 MHz.
4. Taking the N value from Step 3 and the given stroke, use the graph in Figure A-1 to determine
the update time.
5. If the update time is unacceptable, select a lower N value which yields a clock frequency fc of
56 MHz or less. Then recheck the update time.
You can make a note of the parameters as you go along:
Number of bits required:
Resolution (R):
Circulations (N):
Update Time: less than ms.
NOTE:
The following additional steps are pre-
ferred, to increase output stability:
a. Divide the required resolution by 2
b. Select the number of bits from Table
1A, using the new resolution.
c. Discard or do not connect to the least
significant bit.
d. Do not exceed 18 bits (to avoid using
an additional counter card.)
FORMULA:
f
c
= (0.11 x D) ÷ [R (inches) x N] or
f
c
= (2.8 x D) ÷ [R (mm) x N]
where
f
c
= Counter Card clock frequency in MHz
(maximum 56 MHz)
R = Resolution (inches or millimeters)
N = Number of circulations
D = Counter Card divider (1, 2, or 4 only)
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