42
Table 3A
Maximum Stroke Length vs. Number of Significant Bits
X BCD Value Required
(maximum stroke reading) of ‘X’ Number of Bits
7.999 (8) 0111 . 1001 1001 1001 15
9.999 (10) 1001 . 1001 1001 1001 16
19.999 (20) 0001 1001 . 1001 1001 1001 17
39.999 (40) 0011 1001 . 1001 1001 1001 18 *
79.999 (80) 0111 1001 . 1001 1001 1001 19 *
99.999 (100) 1001 1001 . 1001 1001 1001 20 *
199.999 (200) 0001 1001 1001 . 1001 1001 1001 21 *
* A second Digital Counter Card is required for all values requiring 18 bits or more.
PROCEDURE III
System Sizing/BCD Output - “Standard” Resolutions (Using a 27-28 MHz Clock Crystal)
A 27-28 MHz clock crystal can be used to generate 0.001 in. and 0.1 mm resolutions, satisfying
the following resolution requirements: 0.1 in., 0.01 in., 0.001 in, 1 mm, and 0.1 mm. For other res-
olutions, use procedure IV.
Take the following steps to determine the number of bits, circulations, update time, and counter
card divider:
1. Select the circulation number N from Table 4A, using the calculated values. Begin by using the
values in the first column (for counter card divider D = 2).
Table 4A
Recirculation Values for Selected Resolution
Resolution (R) Recirculations (N)
D = 2 D = 1 Remarks
0.1 in. N/A N/A Use 0.001 in. resolution and discard the two least significant digits.
0.01 in. N/A N/A Use 0.001 in. resolution and discard the least significant digit.
0.001 in. 8 4
1 mm N/A N/A Use 0.1 mm resolution and discard the least significant digit.
0.1 mm 2 1
2. Using the N value 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, try Step 1 again, using the values for D = 1. The divider D = 2 is
preferred, to prevent instability of the least significant digit (LSD). If one or more digits are dis-
carded, 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.
NOTE:
If the number of bits required is 18 or
more (requiring two counter cards), and
the desired resolution is 0.1 inch, 0.01
inch, or 1 mm, then consider the alter-
nate procedure in Section IV.
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