43
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.
PROCEDURE IV
System Sizing for BCD Output - Other Resolutions/Non-Standard Clock Crystal
For 0.1 in., 0.0001 in., 0.01 mm, and 0.001 mm, a non-standard counter card clock crystal must be
estimated using the following procedure.
The crystal frequency for a given resolution versus circulations is approximated by the following
formula.
Take the following steps:
1. Select an N (circulation) value using Table 5A for the resolutions shown. These pre-calculated
values are normally sufficient. As an alternative, N values can be calculated using the formulas
above. Begin by using the values from the first column (for counter card divider D = 4). If
none are available under D = 4, then use values from the next column (D = 2).
2. Using the N selected, look up the update time in the graph, Figure A-1. If this update time is
acceptable, record the values for N, R, D, and update time, and go on to Step 3. If this update
time is not acceptable, use the formula above to calculate values for N and try Step 1 again,
using the values for D = 2, then, if necessary, D = 1. The higher divider numbers are preferred,
to prevent instability of the least significant digit (LSD). If one or more digits are discarded,
however, D = 2 offers only marginal improvement over D = 1.
3. Use Table 3A to determine the number of BCD bits required to generate the given resolution.
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
R = Resolution (inches or millimeters)
N = Number of circulations
D = Counter Card divider (1, 2, or 4 only)
NOTE:
Procedure IV should be used only when
absolutely necessary. Ordering a non-
standard clock crystal will add approxi-
mately four weeks to normal manufac-
turing lead times. An additional nomi-
nal charge also applies. Procedure III
above should be used whenever possible.
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