Function of an Enable Input on a Multiplexer Chip
Enable Input Overview The enable input on a multiplexer (MUX) chip serves as a global control signal that determines whether the multiplexer is active or inactive. When the enable input is activated, the multiplexer functions normally, routing one of its input signals to the output based on the selection lines. When the enable input is deactivated, the multiplexer output is disabled, which typically means it outputs a fixed value (often logic LOW or HIGH-Z/tri-state, depending on the chip design)
. Key Functions of the Enable Input
- Global On/Off Switch: The enable input acts as an on/off switch for the entire multiplexer. When enabled, the chip operates as intended; when disabled, the output is either forced to a default state (such as logic 0) or disconnected (high impedance), regardless of the selection lines or data inputs
- Control for Bus Systems: In systems where multiple multiplexers share a common output line or bus, the enable input allows only one multiplexer to drive the bus at a time, preventing signal conflicts. Disabling the unused multiplexers puts their outputs in a high-impedance state (for tri-state outputs), allowing safe bus sharing
- Expansion and Cascading: The enable input is useful when expanding multiplexers to handle more inputs. It allows for coordinated control when multiple multiplexers are cascaded or combined to create larger selection networks
Active-High vs. Active-Low Enable
- The enable input can be either active-high or active-low:
- Active-high enable : The multiplexer is active when the enable input is HIGH (logic 1).
- Active-low enable : The multiplexer is active when the enable input is LOW (logic 0)
- The specific logic level required for activation depends on the chip's design and is typically indicated in the datasheet.
Summary Table
Enable Input State| Multiplexer Output Behavior
---|---
Enabled| Selected input routed to output
Disabled| Output is fixed (e.g., 0 or High-Z)
Conclusion The enable input on a multiplexer chip provides essential control, allowing the chip to be activated or deactivated as needed for system flexibility, bus management, and circuit expansion
