high Z inputs

[john]

Posted on July 30, 2008 at 12:05

high Z inputs

[john]

Posted on May 17, 2011 at 12:40

Just a quick one.

We want to configure a high Z pin, so the best way is :-

GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AIN;

Is that correct ?

And what typical value would the Z be ? (I can't find it in any

data sheet, so please let me know in which PDF I would also find

it).

Thanks,

John.

[asterix]

Posted on May 17, 2011 at 12:40

Hi,

This is correct [ very quick one :) ] , In the Reference Manual RM0008 from ST this mode is called : High impedance-Analog Input,

See Section : 7.1.10 Analog input configuration

When the I/O Port is programmed as Analog Input Configuration:

â—� The Output Buffer is disabled.

â—� The Schmitt Trigger Input is de-activated providing zero consumption for every analog value of the I/O pin. The output of the Schmitt Trigger is forced to a constant value (0).

â—� The weak pull-up and pull-down resistors are disabled.

� Read access to the Input Data Register gets the value “0�.

The Figure 15 on page 101 shows the High impedance-Analog Input Configuration of the I/O Port bit.

When reading this input, you gets 0.

Warmest regards,

Magigimix.

[lanchon]

Posted on May 17, 2011 at 12:40

yes, that's the best option for analog pins, which are not 5V tolerant.

for other pins you could set them to input mode and risk problems if the input voltages are not digital. however maybe the schmitt triggers on these non-analog pins can also be turned of by configuring the pins as ''analog''. this would be a very good option to handle unused 5V pins.

I asked about this a while back but no one from ST answered. if it's important someone could test it: hook a resistive divider to several 5V pins and compare power consumption with the pins in input and analog modes.