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74HC257N Datasheet(PDF) 2 Page - NXP Semiconductors |
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74HC257N Datasheet(HTML) 2 Page - NXP Semiconductors |
2 / 13 page 1998 Sep 30 2 Philips Semiconductors Product specification Quad 2-input multiplexer; 3-state 74HC/HCT257 FEATURES • Non-inverting data path • 3-state outputs interface directly with system bus • Output capability: bus driver • ICC 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; Tamb =25 °C; tr =tf = 6 ns Notes 1. CPD is used to determine the dynamic power dissipation (PD in µW): PD =CPD × VCC2 × fi +∑ (CL × VCC2 × fo) where: fi = input frequency in MHz fo = output frequency in MHz ∑ (CL × VCC2 × fo) = sum of outputs CL = output load capacitance in pF VCC = supply voltage in V 2. For HC the condition is VI = GND to VCC For HCT the condition is VI = GND to VCC − 1.5 V SYMBOL PARAMETER CONDITIONS TYPICAL UNIT HC HCT tPHL/ tPLH propagation delay CL = 15 pF; VCC =5 V nI0, nI1 to nY 11 13 ns S to nY 14 17 ns CI input capacitance 3.5 3.5 pF CPD power dissipation capacitance per multiplexer notes 1 and 2 45 45 pF |
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