HD74ACT161 Datasheet, PDF (3/14 Pages) Hitachi Semiconductor – Synchronous Presettable Binary Counter

HD74ACT161/HD74ACT163
Pin Names
CEP
CET
CP
MR (HD74ACT161)
SR (HD74ACT163/HD74ACT163)
P₀ to P₃
PE
Q₀ to Q₃
TC
Count Enable Parallel Input
Count Enable Trickle Input
Clock Pulse Input
Asynchronous Master Reset Input
Synchronous Reset Input
Parallel Data Inputs
Parallel Enable Input
Flip-Flop Outputs
Terminal Count Output
Functional Description
The HD74ACT161 and HD74ACT163 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 parallel through a clock buffer.
Thus all changes of the Q outputs (except due to Master Reset of the HD74ACT161) occur as a reset 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: asynchronous reset (HD74ACT161),
synchronous reset (HD74ACT163), parallel load, countup and hold. Five control inputs – Master Reste
(MR, HD74ACT161), Synchronous Reset (SR, HD74ACT163), Parallel Enable (PE), Count Enable
Parallel (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 asynchronously forces all outputs Low.
A Low signal on SR 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 (HD74ACT161)
or SR (HD74ACT163) High, CEP and CET permit counting when both are High. Conversely, a Low
signal on either CEP or CET inhibits counting.
The HD74ACT161 and HD74ACT163 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 counter is in state 15. To implement synchronous multistage counters, the TC
outputs can be used with the CEP and CET inputs in two different ways. The TC output is subject to
decoding spikes due to internal race conditions and is therefore not recommended for use as a clock or
asynchronous reset for flip-flops, counters or registers.
Logic Equations: Count Enable = CEP•CET•PE
TC = Q₀•Q₁•Q₂•Q₃•CET
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