Motorola SN54LS155J, SN54LS156J, SN74LS156N, SN74LS155D, SN74LS155N Datasheet

DUAL 1-OF-4 DECODER/

DEMULTIPLEXER

The SN54/74LS155 and SN54/74LS156 are high speed Dual 1-of-4 Decoder/Demultiplexers. These devices have two decoders with common 2-bit Address inputs and separate gated Enable inputs. Decoder ªaº has an Enable gate with one active HIGH and one active LOW input. Decoder ªbº has two active LOW Enable inputs. If the Enable functions are satisfied, one output of each decoder will be LOW as selected by the address inputs. The LS156 has open collector outputs for wired-OR (DOT-AND) decoding and function generator applications.

The LS155 and LS156 are fabricated with the Schottky barrier diode process for high speed and are completely compatible with all Motorola TTL families.

•Schottky Process for High Speed

•Multifunction Capability

•Common Address Inputs

•True or Complement Data Demultiplexing

•Input Clamp Diodes Limit High Speed Termination Effects

•ESD > 3500 Volts

CONNECTION DIAGRAM DIP (TOP VIEW)

VCC			Eb		Eb		A0		O3b		O2b		O1b		O0b
	16		15		14		13		12		11		10		9

NOTE:

The Flatpak version has the same pinouts

(Connection Diagram) as the Dual In-Line Package.

	1		2				3		4		5		6		7		8
	Ea			Ea			A1		O3a		O2a		O1a		O0a		GND

PIN NAMES				LOADING (Note a)
				HIGH		LOW
A0, A1			Address Inputs	0.5	U.L.	0.25	U.L.
Ea, Eb			Enable (Active LOW) Inputs	0.5	U.L.	0.25	U.L.
Ea			Enable (Active HIGH) Input	0.5	U.L.	0.25	U.L.
O0 ± O3			Active LOW Outputs (Note b)	10	U.L.	5 (2.5)	U.L.

NOTES:

a)1 TTL Unit Load (U.L.) = 40 μA HIGH/1.6 mA LOW.

b)The Output LOW drive factor is 2.5 U.L. for Military (54) and 5 U.L. for Commercial (74) Temperature Ranges. The HIGH level drive for the LS156 must be established by an external resistor.

SN54/74LS155

SN54/74LS156

DUAL 1-OF-4 DECODER/

DEMULTIPLEXER

LS156-OPEN-COLLECTOR

LOW POWER SCHOTTKY

			J SUFFIX
			CERAMIC
			CASE 620-09
16	1
			N SUFFIX
			PLASTIC
16			CASE 648-08
	1
			D SUFFIX
	16		SOIC
			CASE 751B-03
		1

ORDERING INFORMATION

SN54LSXXXJ Ceramic

SN74LSXXXN Plastic

SN74LSXXXD SOIC

LOGIC SYMBOL

	1	2		13 3		14 15
		E		A0	A0	E
DECODER			a	A1	A1	DECODER b
0	1	2		3	0	1	2	3
7	6	5		4	9	10	11	12
				VCC = PIN 16
				GND =	PIN	8

FAST AND LS TTL DATA

5-262

SN54/74LS155 •SN54/74LS156

LOGIC DIAGRAM

	Ea Ea		A0 A1		EbEb
1	2	13	3	14	15

VCC = PIN 16
GND =	PIN	8	7	6	5	4	9	10	11	12
=	PIN	NUMBERS	O0a	O1a	O2a	O3a	O0b	O1b	O2b	O3b

FUNCTIONAL DESCRIPTION

The LS155 and LS156 are Dual 1-of-4 Decoder/Demultiplexers with common Address inputs and separate gated Enable inputs. When enabled, each decoder section accepts the binary weighted Address inputs (A0, A1) and provides four mutually exclusive active LOW outputs (O0 ±O3). If the Enable requirements of each decoder are not met, all outputs of that decoder are HIGH.

Each decoder section has a 2-input enable gate. The enable gate for Decoder ªaºrequires one active HIGH input and one active LOW input (Ea•Ea). In demultiplexing applications, Decoder ªaº can accept either true or complemented data by using the Ea or Ea inputs respectively. The enable gate

for Decoder ªbº requires two active LOW inputs (E•E ). The b b

LS155 or LS156 can be used as a 1-of-8 Decoder/Demultiplexer by tying Ea to Eb and relabeling the common connection as (A2). The other Eb and Ea are connected together to form the common enable.

The LS155 and LS156 can be used to generate all four minterms of two variables. These four minterms are useful in some applications replacing multiple gate functions as shown in Fig. a. The LS156 has the further advantage of being able to

AND the minterm functions by tying outputs together. Any number of terms can be wired-AND as shown below.

f = (E + A0 + A1) (E + A0 + A1) (E + A0 + A1) (E + A0 + A1)

where E = Ea + Ea; E = Eb + Eb

EE

A0	O0	A0	O0
A1		A1
E		E
A0	O1	A0	O1
A1		A1
E		E
A0	O2	A0	O2
A1		A1
E		E
A0	O3	A0	O3
A1		A1

Figure a

TRUTH TABLE

ADDRESS

ENABLE ªaº

OUTPUT ªaº

ENABLE ªbº

OUTPUT ªbº

A0

A1

Ea

Ea

O0

O1

O2

O3

Eb

Eb

O0

O1

O2

O3

X

X

L

X

H

H

H

H

H

X

H

H

H

H

X

X

X

H

H

H

H

H

X

H

H

H

H

H

L

L

H

L

L

H

H

H

L

L

L

H

H

H

H

L

H

L

H

L

H

H

L

L

H

L

H

H

L

H

H

L

H

H

L

H

L

L

H

H

L

H

H

H

H

L

H

H

H

L

L

L

H

H

H

L

H = HIGH Voltage Level

L = LOW Voltage Level

X = Don't Care

FAST AND LS TTL DATA

5-263