What Is an Enable Pin?

Hey folks,

Lately, I've been diving into the world of phased array sonar and trying to wrap my head around how it all works. My curiosity was piqued by a captivating video I stumbled upon: https://www.youtube.com/watch?v=z4uxC7ISd-c.

As I delved deeper, I stumbled upon some codes by BitLuni, which you can find here: https://github.com/bitluni/SonarScannerV1/blob/main/ArraySweepESP32/ArraySweepESP32.ino.

digitalWrite(enablePin, 1);  // Turn on output
unsigned long t = 0;
unsigned long ot = ESP.getCycleCount();
while (true) {
  // ... (code details)
}
digitalWrite(enablePin, 0);  // Turn off output

Something interesting I noticed in these codes is the use of an "enable pin." This got me thinking about what exactly an enable pin does. I got some insights from ChatGPT, which said, "Use enable pins when you want to turn a whole component, module, or system on or off. It's great for saving power when something's not in use."

I asked for an example and got this code:

const int enablePin = 4;  // Pin to enable/disable
const int ledPin = 5;     // Pin to control an LED

void setup() {
  pinMode(enablePin, OUTPUT);  // Set enablePin as output
  pinMode(ledPin, OUTPUT);     // Set ledPin as output
  digitalWrite(enablePin, HIGH);  // Start with the component (LED) on
}

void loop() {
  // Turn on the component (LED)
  digitalWrite(enablePin, HIGH);
  
  // Do stuff here (like reading data)
  
  // Turn off the component (LED)
  digitalWrite(enablePin, LOW);
  
  // Wait before repeating
  delay(1000);
}

However, I couldn't figure out the connection between the enablePin and the ledPin in the code. This made me wonder about the point of an enable pin in hardware programming. Coming from a software background, it seems more like a "nice to have" thing than a must. But since I've seen it used multiple times, I'm here to understand its purpose and when it's really needed.

I'd really appreciate it if you could help me get a better grasp of this. What's the real deal with an enable pin in hardware programming? Is it actually helpful, and when should I use it?

Thanks a bunch for your insights and guidance on this matter!

Enable pins are used when multiple devices share some other resources - e,g, data pins, control signals etc.

By selecting the desired device with ‘enable’, only that device responds to the control commands on those shared pins,

In another example, ‘enable’ is slightly misnamed - e.g. some stepper drivers.

Some drivers use the enable pin to perform the single step action, which is correct, but confuses newbies.. This is also often called the ‘step’ pin.

That is because ChatGPT did not provide you with a schematic how it is all wired. For the ChatGPT example you can look at the below.

Below image comes from a datasheet of a 74HC125 IC (https://www.diodes.com/assets/Datasheets/74HC125.pdf).

image

There are 3 pins,

  1. Output Enable pin.
  2. An input pin (A).
  3. An output pin (Y).

The triangle reflects a buffer; the little circle indicates that the OE signal is inverted meaning that a logic 0 "enables" the circuit and a logic 1 "disables" the circuit; this is also indicated by the horizontal line above the letters OE.

If you make the output enable pin LOW, the signal on the input pin propagates to the output and you can control a LED by writing LOW or HIGH to the input pin.

If you make the output enable pin HIGH, the output goes into, what is known as, tri-state (high impedance (high resistance)). As a result, the signal on the input pin will not propagate to the output pin so changing the input signal will not have an effect.

Because the output pin is in high impedance, barely any current can flow and the LED on the output pin will be off.

Note: the datasheet also contains the so-called truth table
image
Z indicates the tri-state state

For the application in your first code, see the above replies.

It does exactly what it says - it enables something:

  • When that pin is active, the thing is enabled;
  • When that pin is inactive, the thing is disabled.

Note that "active" may mean either high or low:

  • An active-high enable will enable the thing when the pin is high;
  • An active-low enable will enable the thing when the pin is low.

As ChatGPT told you, a common example is to put things to sleep (ie, disable) in order to save power when not needed.

Another common example is the Slave Select (SS; aka Chip Select, CS) line in SPI:

https://learn.sparkfun.com/tutorials/serial-peripheral-interface-spi#chip-select-cs

image

This is an example of an active-low enable.

1 Like

So here's a software example: instead of an enable pin, we have an enable flag - the value of the flag decides whether some function is done (ie, enabled) or not:

bool enable_the_thing;

:
:

if( enable_the_thing )
{
     // The thing is enabled - do it!
     do_the_thing();
}
else
{
     // The thing is not enabled - don't it!
    do_other_things();
}
1 Like

Check this link out: https://www.allacronyms.com/CS/electronics

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