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54LS257 Fiches technique(PDF) 3 Page - Motorola, Inc |
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54LS257 Fiches technique(HTML) 3 Page - Motorola, Inc |
3 / 6 page 5-429 FAST AND LS TTL DATA SN54/74LS257B D SN54/74LS258B FUNCTIONAL DESCRIPTION The LS257B and LS258B are Quad 2-Input Multiplexers with 3-state outputs. They select four bits of data from two sources each under control of a Common Data Select Input. When the Select Input is LOW, the I0 inputs are selected and when Select is HIGH, the I1 inputs are selected. The data on the selected inputs appears at the outputs in true (non- inverted) form for the LS257B and in the inverted form for the LS258B. The LS257B and LS258B are the logic implementation of a 4-pole, 2-position switch where the position of the switch is determined by the logic levels supplied to the Select Input. The logic equations for the outputs are shown below: LS257B Za = E0 • (I1a • S + I0a • S) Zb = E0 • (I1b • S + I0b • S) Zc = E0 • (I1c • S + I0c • S) Zd = E0 • (I1d • S + I0d • S) When the Output Enable Input (E0) is HIGH, the outputs are forced to a high impedance “off” state. If the outputs are tied together, all but one device must be in the high impedance state to avoid high currents that would exceed the maximum ratings. Designers should ensure that Output Enable signals to 3-state devices whose outputs are tied together are designed so there is no overlap. LS258B Za = E0 • (I1a • S + I0a • S) Zb = E0 • (I1b • S + I0b • S) Zc = E0 • (I1c • S + I0c • S) Zd = E0 • (I1d • S + I0d • S) TRUTH TABLE OUTPUT ENABLE SELECT INPUT DATA INPUTS OUTPUTS LS257B OUTPUTS LS258B EO S I0 I1 Z Z H X X X (Z) (Z) L H X L L H L H X H H L L L L X L H L L H X H L H = HIGH Voltage Level L = LOW Voltage Level X = Don’t Care (Z) = High Impedance (off) GUARANTEED OPERATING RANGES Symbol Parameter Min Typ Max Unit VCC Supply Voltage 54 74 4.5 4.75 5.0 5.0 5.5 5.25 V TA Operating Ambient Temperature Range 54 74 – 55 0 25 25 125 70 °C IOH Output Current — High 54 74 – 1.0 – 2.6 mA IOL Output Current — Low 54 74 12 24 mA |
Numéro de pièce similaire - 54LS257 |
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Description similaire - 54LS257 |
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