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I'm going through the 'Electrical Characteristics' section of datasheet of PIC24EP128GP206 to find out minimum and maximum voltages and currents specific to GPIO pins.

While doing so, I came across the terms IOL, IOH in the following section:

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What do the IOL, IOH currents exactly represent? Are these the sourcing / sinking currents associated with the output pins? Why is the IOH limit is mentioned negative?

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Why is the IOH limit is mentioned negative?

It's just a convention thing. Normally currents into the device (supply currents etc.) are attributed positive values therefore, currents from chip pins are given a negative sign.

What do the IOL, IOH currents exactly represent? Are these the sourcing / sinking currents

  • IOL is the current into the pin (sinking) when the pin has a logic level of zero.
  • IOH is the current from the pin (sourcing) when the pin has a logic level of one.

All the data in the table in the question refer to the pins being outputs (3rd column of table).

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For a VOH test, the GPIO must act as a constant-current load, and for a VOL test, the GPIO must act as a constant-current source. Before any pin is connected, the GPIO should be set to source or sink the desired current, then, once the pin under test has been connected a voltage measurement should be performed.

thats how they are calculated from the output driver resistance:

VOH = VCC – IOH * ROH

VOL = IOL * ROL

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