74ACT151SCX

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Logic – Signal Switches, Multiplexers, Decoders continue to play a vital role in the design and operation of numerous circuit designs. The impetus for newer and improved components starts from the practicality of current circuits designs but, more often than not, moves further into the realms of what can be technically achieved. Such is the case of the 74ACT151SCX, a high speed CMOS multi-plexer designed to handle both 4 and 8 line data buses. It is, in essence, a logic chip designed to send two control signals to two digital outputs. This applies various combinations of multiple input signals, thus controlling the valid output signals.

The 74ACT151SCX comes with a configuration of two 8-Bit data ports, each aligned along one side of the chip. Each port consists of 8 lines (A-H ports) oriented towards the corner of the chip. The top port (D1) handles 8-Bit data from B0 through to B7, while the lower port (D2) handles 8-Bit data from A0 through to A7. Along the sides of the chip, one finds that the 74ACT151SCX has three distinct signal lines; select 1 (S1), select 2 (S2), and enable (EN). Furthermore, each port has an enable signal line that acts as a global enable for the lower D2 port.

In operation, a logic \'0\' signal applied to the select 1 (S1) and select 2 (S2) signal lines enables the 74ACT151SCX to transfer the data signals from either the A port (D2) or the B port (D1) to the output. A logic \'0\' signal present on the enable (EN) signal line prevents any signal transference, thus providing an additional level of control over the device. When both S1 and S2 are \'1\', the device is disabled and all outputs (QA to QH) are forced to a logic \'0\' regardless of the inputs (A0 to A7 and B0 to B7).

The logic levels for the control signals (S1, S2 and EN) of the 74ACT151SCX follow the voltage levels established for TTL (Transistor-Transistor Logic), Low-Power Schottky TTL (LP-TTL) and TTL-IAS (TTL with Input Assist level-shifting). Circuit designers should take into consideration the fact that the control signals will enter through Schottky diodes to form the clamping-style logic inputs and, thus, the logic levels should not be allowed to drop into the forward voltage region of the Schottky diodes, as this will exceed the specified logic threshold for the device.

As for power supply design and selection, there are a few things to take into consideration. First of all, one should make sure that the Vcc voltage is between 4.5 and 5.5V. Secondly, one should take into consideration the Pd (Power Dissipation) of each component used. The 74ACT151SCX has a total Pd of 100mW and the application of a current regulator is recommended for further protection of the device.

The 74ACT151SCX is an effective component for multiplexing data buses and works well in applications with multiple input and output signals. As its name implies, the 74ACT151SCX is part of the 74ACT 151 family of multiplexers, which promise data transfers up to 20X faster than their predecessors. The 74ACT151SCX is designed to minimize power consumption and deliver high speed performance in areas like peripheral control, high end instrumentation, portable electronics and other applications.

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