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I am working on dc motor speed control project in which I am using 12 v dc motor , l293d motor driver ic and pic16f877A for controlling the motor.

Pic16f877A is sending pwm signal from its RC2 pin(pin17) which i have connected to pin2 of motor driver ic L293d.

But i noticed that even when my enable pin is not connected to source(vdd or gnd) L293d is still working and motor shaft spins.

How can motor driver ic L293d works when my enable pin is not connected.

But when i connect it to ground it doesn't work . So is enable pin of L293d by default high??

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  • \$\begingroup\$ Enable pin must have higher potatial than gnd arbitrarily, you can figure it out by using voltmeter. \$\endgroup\$ – SOKRATES Mar 31 '15 at 18:21
  • \$\begingroup\$ i have not connected enable pin but l293d still works ,the motor is working how?? \$\endgroup\$ – dcmotor Mar 31 '15 at 18:23
  • \$\begingroup\$ it is sufficient to enable l293d by having voltage difference between gnd and enable pins even if you dont connect enable pin to anywhere as i said if you connected gnd to L293 it will create voltage differance,but you should dedicate this difference with pwm,more difference more output voltage to motor. Use multimeter and see. \$\endgroup\$ – SOKRATES Mar 31 '15 at 18:33
  • \$\begingroup\$ @dcmotor Please update your post so that it looks more like standard English writing and doesn't cause eyes to bleed. Some of us lazy volunteers don't like when eyes bleed. \$\endgroup\$ – Nick Alexeev Mar 31 '15 at 19:32
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The L293D doesn't need anything connected to the enable pin(s) in order to enable it. Read the data sheet and look at diagram on page 3: -

enter image description here

Until you start drawing current to ground from the input the PNP BJT won't be conducting.

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