TM 11 5895-1096-40
Table 2-1. U7 Output Table
Table 2-3. Code Selector Switch Truth Table.
Counter State
U7B-15
U7A-1
Switch Position
A
B
C
D
0 (hnds)
0
0
0
1 (tens)
1
0
1
X
2 (units)
0
1
2
X
3
X
X
4
X
Table 2-2. U7, UI Truth Table
5
X
X
6
X
X
Counter State
U7B-15
U7A-2
U1C-11
7
X
X
X
0
0
1
1
8
X
1
1
1
0
9
X
X
2
0
0
0
Figure 2-2. Code Selector Switch Diagram.
e. Multiplexer, (U4) (fig. 2-3). This IC is a dual four bit
four data bits in the 1, 2, 4, and 8 bit sequence, then the tens
digit switch is enabled and the multiplexer will sample the four
multiplexer. It operates as a two pole, four position switch that
new data bits. This sequence will continue for the units digit,
is capable of passing a signal in either direction. The position
then repeat.
that the multiplexer selects is determined by the binary value
(b) Since U4 is a bilateral device, it will
of the A and B inputs (pins 10 and 9).
pass a signal in either direction. R17, the load resistor for the
(1) The first half of the U4 is used to sequentially
switch mounted diodes, is connected to the output Y. Due to
select the four bits of NBCD data coming from the selector
interconnect wiring capacitance and the NBCD data filters R7
switches. The A and B inputs to U4 are the outputs from the
through R10 and C3 through C6, the NRZ word at U4-13 will
divide-by-four counter (U5A, U5B) that are counting in
not be an ideal signal. Many glitches will be present and the
descending order. These inputs control the sequence of U4,
waveform edges will be rounded.
causing U4 to commutate in the descending order of Y3 to YO
(3) The remaining half of U4 is wired to provide
that is wired to select the NBCD data A to D. The output Y
the AND function of the D data bit and the units digit. The X
from U4 will be NRZ code as selected on the front panel
output will be a positive pulse indicating the last data bit of
CODE SELECTOR switches.
each code word.
(2) This serial code is generated by the
f. Delay Flip-flop U3A and U3B. This IC is a dual D
combination of the multiplexer and the divide-by-three switch
strobes that provide the following sequence:
(data type) flip-flop and is used to synchronize the two outputs
(a) While the hundreds switch is enabled
from the multiplexer. This has the effect of restoring these
by the hundreds strobe, the multiplexer will sample each of the
signals to the ideal digital waveforms.
2-3
