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HD74ACT161/HD74ACT163
Synchronous Presettable Binary Counter
Description
The HD74ACT161 and HD74ACT163 are high-speed synchronous modulo-16 binary counters. They are synchronously presettable for application in programmable dividers and have two types of Count Enable inputs plus a Terminal Count output for versatility in forming synchronous multistage counters. The HD74ACT161 have an asynchronous Master Reset input that overrides all other inputs and forces the outputs Low. The HD74ACT163 has a Synchronous Reset input that overrides counting and parallel loading and allows the outputs to be simultaneously reset on the rising edge of the clock.
Features
• • • • • Synchronous Counting and Loading High-Speed Synchronous Expansion Typical Count Rate of 125 MHz Outputs Source/Sink 24 mA HD74ACT161 and HD74ACT163 have TTL-Compatible Inputs
HD74ACT161/HD74ACT163
Pin Arrangement
*R 1 CP 2 P0 3 P1 4 P2 5 P3 6 CEP 7 GND 8 (Top view)
16 VCC 15 TC 14 Q0 13 Q1 12 Q2 11 Q3 10 CET 9 PE
Logic Symbol
PE P0 P1 P2 P3 CEP CET CP *R Q0 Q1 Q2 Q3 * • MR for HD74ACT161 • SR for HD74AC163/HD74ACT163 TC
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HD74ACT161/HD74ACT163
Pin Names
CEP CET CP MR (HD74ACT161) SR (HD74ACT163/HD74ACT163) P 0 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 = Q 0•Q1•Q2•Q3•CET
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HD74ACT161/HD74ACT163
Mode Select Table
SR * 1 L H H H H Note: PE X L H H H CET X X H L X CEP X X H X L Action on the Rising Clock Edge ( Reset (Clear) Load (Pn → Qn) Count (Increment) No change (Hold) No change (Hold) )
1. For HD74AC163/HD74ACT163 H : High Voltage Level L : Low Voltage Level X : Immaterial
State Diagram
0 1 2 3 4
15
5
14
6
13
7
12
11
10
9
8
4
HD74ACT161/HD74ACT163
Block Diagram
P0 PE ’161 ’163 CEP CET ’163 ONRY TC P1 P2 P3
CP
CP
’161 ONRY
CP D CP D CD O O
Q0
Q0 DETAIL A
DETAIL A
DETAIL A
DETAIL A
MR ’161 SR ’163 Q0 Q1 Q2 Q3
Please note that this diagram is provided only for the understanding of logic operations and should not be used to estimate propagation delays.
DC Characteristics (unless otherwise specified)
Item Maximum quiescent supply current Maximum quiescent supply current Maximum additional ICC/input (HD74ACT161/HD74ACT163) Symbol I CC I CC I CCT Max 80 8.0 1.5 Unit µA µA mA Condition VIN = VCC or ground, VCC = 5.5 V, Ta = Worst case VIN = VCC or ground, VCC = 5.5 V, Ta = 25°C VIN = VCC – 2.1 V, VCC = 5.5 V, Ta = Worst case
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HD74ACT161/HD74ACT163
AC Characteristics: HD74ACT161
Ta = +25°C CL = 50 pF Item Maximum count frequency Propagation delay CP to Qn (PE Input HIGH or LOW) Propagation delay CP to Qn (PE Input HIGH or LOW) Propagation delay CP to TC Propagation delay CP to TC Propagation delay CET to TC Propagation delay CET to TC Propagation delay MR to Q n Propagation delay MR to TC Note: Sy.