74HC257 Datasheet, PDF (2/13 Pages) NXP Semiconductors – Quad 2-input multiplexer 3-state

Philips Semiconductors
Quad 2-input multiplexer; 3-state
Product specification
74HC/HCT257
FEATURES
• Non-inverting data path
• 3-state outputs interface directly with system bus
• Output capability: bus driver
• I_CC category: MSI
GENERAL DESCRIPTION
The 74HC/HCT257 are high-speed Si-gate CMOS devices
and are pin compatible with low power Schottky TTL
(LSTTL). They are specified in compliance with JEDEC
standard no. 7A.
The 74HC/HCT257 have four identical 2-input multiplexers
with 3-state outputs, which select 4 bits of data from two
sources and are controlled by a common data select
input (S).
The data inputs from source 0 (1I₀ to 4I₀) are selected
when input S is LOW and the data inputs from source 1
(1I₁ to 4I₁) are selected when S is HIGH. Data appears at
the outputs (1Y to 4Y) in true (non-inverting) form from the
selected inputs.
The “257” is the logic implementation of a 4-pole,
2-position switch, where the position of the switch is
determined by the logic levels applied to S. The outputs
are forced to a high impedance OFF-state when OE is
HIGH.
The logic equations for the outputs are:
1Y = OE.(1I₁.S + 1I₀.S)
2Y = OE.(2I₁.S + 2I₀.S)
3Y = OE.(3I₁.S + 3I₀.S)
4Y = OE.(4I₁.S + 4I₀.S)
The “257” is identical to the “258” but has non-inverting
(true) outputs.
QUICK REFERENCE DATA
GND = 0 V; T_amb = 25 °C; t_r = t_f = 6 ns
SYMBOL
PARAMETER
CONDITIONS
TYPICAL
HC
HCT
t_PHL/ t_PLH
propagation delay
nI₀, nI₁ to nY
S to nY
C_L = 15 pF; V_CC = 5 V
11
13
14
17
C_I
input capacitance
3.5
3.5
C_PD
power dissipation capacitance per multiplexer notes 1 and 2
45
45
Notes
1. C_PD is used to determine the dynamic power dissipation (P_D in µW):
P_D = C_PD × V_CC2 × f_i + ∑ (C_L × V_CC2 × f_o) where:
f_i = input frequency in MHz
f_o = output frequency in MHz
∑ (C_L × V_CC2 × f_o) = sum of outputs
C_L = output load capacitance in pF
V_CC = supply voltage in V
2. For HC the condition is V_I = GND to V_CC
For HCT the condition is V_I = GND to V_CC − 1.5 V
UNIT
ns
ns
pF
pF
1998 Sep 30
2