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SN54LS251 数据表(PDF) 2 Page - Motorola, Inc |
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SN54LS251 数据表(HTML) 2 Page - Motorola, Inc |
2 / 6 page 5-411 FAST AND LS TTL DATA SN54/74LS251 FUNCTIONAL DESCRIPTION The LS251 is a logical implementation of a single pole, 8-position switch with the switch position controlled by the state of three Select inputs, S0, S1, S2. Both assertion and negation outputs are provided. The Output Enable input (EO) is active LOW. When it is activated, the logic function provided at the output is: Z = EO ⋅ (I0 ⋅ S0 ⋅ S1 ⋅ S2 + I1 ⋅ S0 ⋅ S1 ⋅ S2 + I2 ⋅ S0 ⋅ S1 ⋅ Z = EO ⋅ S2 + I3 ⋅ S0 ⋅ S1⋅ S2 + I4 ⋅ S0 ⋅ S1 ⋅ S2 + I5 ⋅ S0 ⋅ Z = EO ⋅ S1 ⋅ S2 + I6 ⋅ S0 ⋅ S1 ⋅ S2 + I7 ⋅ S0 ⋅ S1 ⋅ S2). When the Output Enable is HIGH, both outputs are in the high impedance (high Z) state. This feature allows multiplexer expansion by tying the outputs of up to 128 devices together. When the outputs of the 3-state devices are tied together, all but one device must be in the high impedance state to avoid high currents that would exceed the maximum ratings. The Output Enable signals should be designed to ensure there is no overlap in the active LOW portion of the enable voltage. TRUTH TABLE E0 S2 S1 S0 I0 I1 I2 I3 I4 I5 I6 I7 Z Z H X X X X X X X X X X X (Z) (Z) L L L L L X X X X X X X H L L L L L H X X X X X X X L H L L L H X L X X X X X X H L L L L H X H X X X X X X L H L L H L X X L X X X X X H L L L H L X X H X X X X X L H L L H H X X X L X X X X H L L L H H X X X H X X X X L H L H L L X X X X L X X X H L L H L L X X X X H X X X L H L H L H X X X X X L X X H L L H L H X X X X X H X X L H L H H L X X X X X X L X H L L H H L X X X X X X H X L H L H H H X X X X X X X L H L L H H H X X X X X X X H L H 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 4.75 5.0 5.25 V TA Operating Ambient Temperature Range 0 25 70 °C IOH Output Current — High – 2.6 mA IOL Output Current — Low 24 mA |
类似零件编号 - SN54LS251 |
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类似说明 - SN54LS251 |
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