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74LVX163 Datasheet(PDF) 2 Page - National Semiconductor (TI)

[Old version datasheet] Texas Instruments acquired National semiconductor.
Part No. 74LVX163
Description  Low Voltage Synchronous Binary Counter with Synchronous Clear
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Manufacturer  NSC [National Semiconductor (TI)]
Direct Link  http://www.national.com
Logo NSC - National Semiconductor (TI)

74LVX163 Datasheet(HTML) 2 Page - National Semiconductor (TI)

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Functional Description
The LVX163 counts in modulo-16 binary sequence From
state 15 (HHHH) it increments to state 0 (LLLL) The clock
inputs of all flip-flops are driven in parallel through a clock
buffer Thus all changes of the Q outputs occur as a result
of and synchronous with the LOW-to-HIGH transition of
the CP input signal The circuits have four fundamental
modes of operation in order of precedence synchronous
reset parallel load count-up and hold Four control inputs
Synchronous Reset (MR) Parallel Enable (PE) Count En-
able Parallel (CEP) and Count Enable Trickle (CET)deter-
mine the mode of operation as shown in the Mode Select
Table A LOW signal on MR overrides counting and parallel
loading and allows all outputs to go LOW on the next rising
edge of CP A LOW signal on PE overrides counting and
allows information on the Parallel Data (Pn) inputs to be
loaded into the flip-flops on the next rising edge of CP With
PE and MR HIGH CEP and CET permit counting when both
are HIGH Conversely a LOW signal on either CEP or CET
inhibits counting
The LVX163 uses D-type edge-triggered flip-flops and
changing the MR PE CEP and CET inputs when the CP is
in either state does not cause errors provided that the rec-
ommended setup and hold times with respect to the rising
edge of CP are observed
The Terminal Count (TC) output is HIGH when CET is HIGH
and counter is in state 15 To implement synchronous multi-
stage counters the TC outputs can be used with the CEP
and CET inputs in two different ways
Figure 1 shows the connections for simple ripple carry in
which the clock period must be longer than the CP to TC
delay of the first stage plus the cumulative CET to TC de-
lays of the intermediate stages plus the CET to CP setup
time of the last stage This total delay plus setup time sets
the upper limit on clock frequency For faster clock rates
the carry lookahead connections shown in
Figure 2 are rec-
ommended In this scheme the ripple delay through the in-
termediate stages commences with the same clock that
causes the first stage to tick over from max to min in the Up
mode or min to max in the Down mode to start its final
cycle Since this final cycle takes 16 clocks to complete
there is plenty of time for the ripple to progress through the
intermediate stages The critical timing that limits the clock
period is the CP to TC delay of the first stage plus the CEP
to CP setup time of the last stage The TC output is subject
to decoding spikes due to internal race conditions and is
therefore not recommended for use as a clock or asynchro-
nous reset for flip-flops registers or counters When the
Output Enable (OE) is LOW the parallel data outputs O0
O3 are active and follow the flip-flop Q outputs A HIGH
signal on OE forces O0–O3 to the High Z state but does not
prevent counting loading or resetting
Logic Equations Count Enable e CEP
 CET  PE
TC e Q0  Q1  Q2  Q3  CET
Mode Select Table
MR
PE
CET
CEP
Action on the Rising
Clock Edge (
L )
L
X
X
X
Reset (Clear)
H
L
X
X
Load (Pn
x Qn)
H
H
H
H
Count (Increment)
H
H
L
X
No Change (Hold)
H
H
X
L
No Change (Hold)
H e HIGH Voltage Level
L e LOW Voltage Level
X e Immaterial
State Diagram
TLF12157 – 4
TLF12157 – 5
FIGURE 1
TLF12157 – 6
FIGURE 2
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