74HC157 — Quad 2-to-1 Line Data Selector / Multiplexer (Non-Inverting)

Overview

The 74HC157 (SN74HC157 / 74HCT157) is a high-speed silicon-gate CMOS Quad 2-to-1 line data selector / multiplexer IC manufactured by Texas Instruments, Nexperia, and onsemi. Housed in a standard 16-pin through-hole DIP-16 and surface-mount SOIC-16 / TSSOP-16 package, it contains four independent 2-input digital multiplexers sharing a common Select input ( $S$ ) and a common active-LOW Strobe / Enable input ( $\bar{G}$ ).

Operating across a supply voltage range of $2.0\text{V}$ to $6.0\text{V}$ DC with a rapid propagation delay of $11\text{ ns}$ at $5\text{V}$ , the 74HC157 selects four bits of data from two alternative 4-bit sources ( $A$ or $B$ ) and passes them to the four outputs ( $1Y \dots 4Y$ ). It is a cornerstone building block in retrocomputing architectures (Commodore 64, Apple II, ZX Spectrum) and FPGA/CPLD glue-logic for 4-bit/8-bit bus multiplexing, dynamic RAM (DRAM) row/column address multiplexing, and video signal switching.

Quick reference


Logic Family	High-Speed CMOS (74HC) / TTL-Compatible (74HCT)
Function	Quad 2-Input to 1-Output Data Multiplexer (Non-Inverting)
Channels	4 independent 2-to-1 multiplexers ( $1A/1B \dots 4A/4B$ )
Package	16-pin DIP (DIP-16 / PDIP-16) / 16-pin SOIC / TSSOP-16
Supply Voltage ( $V_{CC}$ )	$2.0\text{ V}$ to $6.0\text{ V}$ (74HC) / $4.5\text{ V} \dots 5.5\text{ V}$ (74HCT)
Propagation Delay ( $t_{pd}$ )	$11\text{ ns}$ typ ( $21\text{ ns}$ max) at $V_{CC} = 5.0\text{ V}$
Output Drive Current ( $I_{OH}/I_{OL}$ )	$\pm 4.0\text{ mA}$ at $5.0\text{ V}$ ( $10\text{ LSTTL}$ load fan-out)
Controls	1 Common Select ( $S$ / $\bar{A}/B$ ), 1 Common Strobe ( $\bar{G}$ )

Pinout (DIP-16 Package)

text

                            ┌───┴───┐
       (Common Select)  S  1│ 1   16│ VCC (+2V to +6V)
       (Mux 1, Input A) 1A 2│       │15 /G / STROBE (Active-Low)
       (Mux 1, Input B) 1B 3│ 74HC  │14 4A (Mux 4, Input A)
       (Mux 1, Output)  1Y 4│  157  │13 4B (Mux 4, Input B)
       (Mux 2, Input A) 2A 5│ DIP-16│12 4Y (Mux 4, Output)
       (Mux 2, Input B) 2B 6│       │11 3A (Mux 3, Input A)
       (Mux 2, Output)  2Y 7│       │10 3B (Mux 3, Input B)
                   GND  8│       │9  3Y (Mux 3, Output)
                            └───────┘

Pin	Name	Type	Description
1	`SELECT`	Digital Input	Common Data Select ( $S$ / $\bar{A}/B$ ); LOW selects $A$ inputs, HIGH selects $B$ inputs
2	`1A`	Digital Input	Multiplexer 1, Input A
3	`1B`	Digital Input	Multiplexer 1, Input B
4	`1Y`	Digital Output	Multiplexer 1, Output
5	`2A`	Digital Input	Multiplexer 2, Input A
6	`2B`	Digital Input	Multiplexer 2, Input B
7	`2Y`	Digital Output	Multiplexer 2, Output
8	`GND`	Power	Common Ground reference ( $0\text{ V}$ )
9	`3Y`	Digital Output	Multiplexer 3, Output
10	`3B`	Digital Input	Multiplexer 3, Input B
11	`3A`	Digital Input	Multiplexer 3, Input A
12	`4Y`	Digital Output	Multiplexer 4, Output
13	`4B`	Digital Input	Multiplexer 4, Input B
14	`4A`	Digital Input	Multiplexer 4, Input A
15	`STROBE`	Digital Input	Active-LOW Common Strobe ( $\bar{G}$ ; tie to GND for normal operation)
16	`VCC`	Power	Positive Supply Voltage ( $+2.0\text{ V}$ to $+6.0\text{ V}$ )

Function / Truth Table

Strobe / Enable ( $\bar{G}$ )	Select ( $S$ )	Input $A$ ( $nA$ )	Input $B$ ( $nB$ )	Output $Y$ ( $nY$ )
H	X	X	X	L (All outputs forced LOW)
L	L	L	X	L ( $nY = nA$ )
L	L	H	X	H ( $nY = nA$ )
L	H	X	L	L ( $nY = nB$ )
L	H	X	H	H ( $nY = nB$ )

Typical Application: 4-Bit Nibble Bus Selector

text

     4-Bit Bus A (A3, A2, A1, A0) ────► [Pins 14, 11, 5, 2: 4A, 3A, 2A, 1A]
     4-Bit Bus B (B3, B2, B1, B0) ────► [Pins 13, 10, 6, 3: 4B, 3B, 2B, 1B]
                                               74HC157
     Control Signal (Select A/B) ─────► [Pin 1: SELECT]
     Enable (GND) ────────────────────► [Pin 15: /G]
                                               │
     Selected 4-Bit Bus Output ◄─────── [Pins 12, 9, 7, 4: 4Y, 3Y, 2Y, 1Y]

Comparison: 74HC157 vs 74HC158 vs 74HC257

IC Part Number	Function	Output Stage	Inverting / Non-Inverting
74HC157	Quad 2-to-1 Multiplexer	Standard Push-Pull	Non-Inverting ( $nY$ )
74HC158	Quad 2-to-1 Multiplexer	Standard Push-Pull	Inverting ( $n\bar{Y}$ )
74HC257	Quad 2-to-1 Multiplexer	3-State (Tri-State)	Non-Inverting ( $nY$ )

Common mistakes

Leaving Strobe Pin 15 ( $\bar{G}$ ) floating: If $\bar{G}$ is disconnected or pulled HIGH, all four outputs ( $1Y \dots 4Y$ ) are forced to logic LOW. Always tie Pin 15 to GND (0V) for continuous multiplexing.
Using 74HC157 for bidirectional data buses: The 74HC157 is strictly a unidirectional multiplexer ( $A/B \to Y$ ). If bidirectional data transmission is needed between buses, use a bus transceiver like the 74HC245.

Notes

Cascading for 8-Bit / 16-Bit Words: Two 74HC157 ICs wired with their Select and Strobe pins in parallel create an instant 8-bit wide 2-to-1 byte selector.

Interface	4 Pairs Data Inputs (1A-4B), 1 Select (S), 1 Strobe (G), 4 Outputs (1Y-4Y)
Supply	2–6 V
Package	16-pin DIP (DIP-16 / PDIP-16) / 16-pin SOIC / 16-pin TSSOP