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74F161A View Datasheet(PDF) - Fairchild Semiconductor

Part Name
Description
Manufacturer
74F161A
Fairchild
Fairchild Semiconductor Fairchild
74F161A Datasheet PDF : 8 Pages
1 2 3 4 5 6 7 8
Functional Description
The 74F161A and 74F163A count in modulo-16 binary
sequence. From state 15 (HHHH) they increment to state 0
(LLLL). The clock inputs of all flip-flops are driven in paral-
lel through a clock buffer. Thus all changes of the Q outputs
(except due to Master Reset of the 74F161A) occur as a
result of, and synchronous with, the LOW-to-HIGH transi-
tion of the CP input signal. The circuits have four funda-
mental modes of operation, in order of precedence:
asynchronous reset (74F161A), synchronous reset
(74F163A), parallel load, count-up and hold. Five control
inputsMaster Reset (MR, 74F161A), Synchronous Reset
(SR, 74F163A), Parallel Enable (PE), Count Enable Paral-
lel (CEP) and Count Enable Trickle (CET)determine the
mode of operation, as shown in the Mode Select Table. A
LOW signal on MR overrides all other inputs and asynchro-
nously forces all outputs LOW. A LOW signal on SR over-
rides 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 ('F161A) or SR
(74F163A) HIGH, CEP and CET permit counting when
both are HIGH. Conversely, a LOW signal on either CEP or
CET inhibits counting.
The 74F161A and 74F163A use D-type edge triggered flip-
flops and changing the SR, PE, CEP and CET inputs when
the CP is in either state does not cause errors, provided
that the recommended 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 the counter is in state 15. To implement synchro-
nous multi-stage counters, the TC outputs can be used
with the CEP and CET inputs in two different ways. Please
refer to the 74F568 data sheet. 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, counters or registers.
Logic Equations: Count Enable = CEP CET PE
TC = Q0 Q1 Q2 Q3 CET
Mode Select Table
SR
(Note 1)
PE
CET
CE
P
 Action on the Rising
Clock Edge ( )
L
X X X Reset (Clear)
H
L X X Load (PnQn)
H
H H H Count (Increment)
H
H L X No Change (Hold)
H
H X L No Change (Hold)
H = HIGH Voltage Level
L = LOW Voltage Level
X = Immaterial
Note 1: For 74F163A only
State Diagram
Block Diagram
3
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