CD54ACT161, CD74ACT161
4-BIT SYNCHRONOUS BINARY COUNTERS
SCHS298 APRIL 2000
1
POST OFFICE BOX 655303
DALLAS, TEXAS 75265
D
Inputs Are TTL-Voltage Compatible
D
Internal Look-Ahead for Fast Counting
D
Carry Output for n-Bit Cascading
D
Synchronous Counting
D
Synchronously Programmable
D
SCR-Latchup-Resistant CMOS Process and
Circuit Design
D
Exceeds 2 kV ESD Protection per
MIL-STD-883, Method 3015
D
Package Options Include Plastic
Small-Outline (M) Standard Plastic (E) and
Ceramic (F) DIPs
description
The CD54ACT161 and CD74ACT161 devices are 4-bit binary counters. These synchronous, presettable
counters feature an internal carry look-ahead for application in high-speed counting designs. Synchronous
operation is provided by having all flip-flops clocked simultaneously so that the outputs change coincident with
each other when so instructed by the count-enable (ENP, ENT) inputs and internal gating. This mode of
operation eliminates the output counting spikes that are normally associated with synchronous (ripple-clock)
counters. A buffered clock (CLK) input triggers the four flip-flops on the rising (positive-going) edge of the clock
waveform.
These devices are fully programmable; that is, they can be preset to any number between 0 and 9 or 15.
Presetting is synchronous; therefore, setting up a low level at the load input disables the counter and causes
the outputs to agree with the setup data after the next clock pulse, regardless of the levels of the enable inputs.
The clear function is asynchronous. A low level at the clear (CLR) input sets all four of the flip-flop outputs low,
regardless of the levels of the CLK, load (LOAD), or enable inputs.
The carry look-ahead circuitry provides for cascading counters for n-bit synchronous applications without
additional gating. Instrumental in accomplishing this function are ENP, ENT, and a ripple-carry output (RCO).
Both ENP and ENT must be high to count, and ENT is fed forward to enable RCO. Enabling RCO produces a
high-level pulse while the count is maximum (9 or 15 with Q
A
high). This high-level overflow ripple-carry pulse
can be used to enable successive cascaded stages. Transitions at ENP or ENT are allowed, regardless of the
level of CLK.
The counters feature a fully independent clock circuit. Changes at control inputs (ENP, ENT, or LOAD) that
modify the operating mode have no effect on the contents of the counter until clocking occurs. The function of
the counter (whether enabled, disabled, loading, or counting) is dictated solely by the conditions meeting the
stable setup and hold times.
The CD54ACT161 is characterized for operation over the full military temperature range of 55
C to 125
C.
The CD74ACT161 is characterized for operation from 40
C to 85
C.
Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of
Texas Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet.
1
2
3
4
5
6
7
8
16
15
14
13
12
11
10
9
CLR
CLK
A
B
C
D
ENP
GND
V
CC
RCO
Q
A
Q
B
Q
C
Q
D
ENT
LOAD
CD54ACT161 . . . F PACKAGE
CD74ACT161 . . . E OR M PACKAGE
(TOP VIEW)
Copyright
2000, Texas Instruments Incorporated
PRODUCTION DATA information is current as of publication date.
Products conform to specifications per the terms of Texas Instruments
standard warranty. Production processing does not necessarily include
testing of all parameters.
CD54ACT161, CD74ACT161
4-BIT SYNCHRONOUS BINARY COUNTERS
SCHS298 APRIL 2000
2
POST OFFICE BOX 655303
DALLAS, TEXAS 75265
FUNCTION TABLE
INPUTS
OUTPUTS
FUNCTION
CLR
CLK
ENP
ENT
LOAD
A,B,C,D
Qn
RCO
FUNCTION
L
X
X
X
X
X
L
L
Reset (clear)
H
X
X
l
l
L
L
Parallel load
H
X
X
l
h
H
Note 1
Parallel load
H
h
h
h
X
Count
Note 1
Count
H
X
l
X
h
X
qn
Note 1
Inhibit
H
X
X
l
h
X
qn
L
Inhibit
H = high level, L = low level, X = don't care, h = high level one setup time prior to the CLK
low-to-high transition, l = low level one setup time prior to the CLK low-to-high transition, q = the
state of the referenced output prior to the CLK low-to-high transition,
= CLK low-to-high
transition.
NOTE 1: The RCO output is high when ENT is high and the counter is at terminal count (HHHH).
logic symbol
This symbol is in accordance with ANSI/IEEE Std 91-1984 and IEC Publication 617-12.
14
13
12
11
CTRDIV16
LOAD
1,5D
3
A
4
B
5
C
6
D
CT=0
1
M2
M1
9
C5/2,3,4+
G3
10
ENT
RCO
15
3CT=15
QA
QB
QC
QD
G4
7
ENP
2
CLK
CLR
[1]
[2]
[4]
[8]
CD54ACT161, CD74ACT161
4-BIT SYNCHRONOUS BINARY COUNTERS
SCHS298 APRIL 2000
5
POST OFFICE BOX 655303
DALLAS, TEXAS 75265
typical clear, preset, count, and inhibit sequence
The following sequence is illustrated below:
1.
Clear outputs to zero (asynchronous)
2.
Preset to binary 12
3.
Count to 13, 14, 15, 0, 1, and 2
4.
Inhibit
Data
Inputs
Data
Outputs
CLR
LOAD
A
B
C
D
CLK
ENP
ENT
RCO
QA
QB
QC
QD
Async
Clear
Preset
Count
Inhibit
12
13
14
15
0
1
2
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