Standard Drive,Low Frequency I/O

[Chaabane]

Hello,

I configured pin P1.15 as output and with GPIO_PIN_CNF_DRIVE_H0H1 but I only get 1.7V ?

Does "standard drive" means that the pins can't get to 3V ?

Thank you

[RK]

No of course it doesn't. This is all in the documentation. It means the current output is limited to about 2mA so let me guess you have a load of somewhere about 850 ohms attached, so at 2mA you get 1.7v across the load. 

[Chaabane]

You guessed right, I have an IC connected to this pin. When I remove the connexion to the IC I get 3V as expected.

But I'm still confused about the meaning of high drive, low drive....

What does  S0S1 : Standard '0', standard '1'  or  H0S1 : High drive '0', standard '1'  mean ?

For example, does H0S1 means : high drive (5mA)  when pin is in low voltage (VSS) and  standard drive (0.5 mA)when pin in high voltage level (VDD) ?

[RK]

That's pretty much what it means. Don't think of voltage, think of current. High drive means 5mA, low drive means 1mA (or 2 .. the specs are quite wide). If the pin is  DRIVEN, ie S0S1 it means a totem pole configuration where the pin is actively pulled to '0' or '1'. So if you have a S0S1 and  you're connected to say a resistor to ground, in the '1' state you'll source max 1mA  of current, in the '0' state you won't sink anything because all the voltages are equal. If however  you're connected to a resistor/LED connected to VDD in that S0S1 config, a '1' won't really do anything, voltages the same, but a '0' will sink up to 1mA of current. So the drive strength tells you how much current can be sourced from or sunk to a given pin if it's connected to something of the 'other' voltage. 

In most cases you only really care about one of those drive strengths, usually you're either sourcing  current at '1' or sinking it at '0' but not both but there are cases in which both matter. 

And then finally there the 'D' drives which basically mean high impedence, the chip just gets out of the way and lets any other driver on the line run the show. S0D1 is what I'd think of as open drain, when high it's basically disconnected so someone else can pull low, when low it's driven, you'd find that kind of drive in TWI for instance. 

Anyway - with drive strength - don't think of voltage, think of current, the connection will do whatever is necessary to keep current within limits, if you have something with low resistance connected, the pin will have high resistance to ensure the current is limited and the drop across the load will be small because of  the effective voltage divider. 

[Chaabane]

Thank you very much for the this. Now everything make sense.