Explanation of different PIO configurations

PIO Configurations

Hi,

what does it mean when a PIO(programmable Input/Output) can be configured as pull up, Open drain, Push-pull and High impedance. Please explain each term. Thanks for the help!

Re: PIO Configurations

Open drain : The FET at output stage is not connected to Vcc. As such, it can only output LOW, but floats the output FET is switched on.

Push-Pull : The common scenario. Means it can go both high and low, ie not Open-Drain.

High Impedence : Virtual open circuit. It's as though the pin was not even connected to the circuit, otherwise known as floating.

The concept of floating is used to share lines among multiple components, ie a data bus. All components will float the bus, and any component is capable of pulling the bus high as long as the bus has a pull-up resistor.

Re: PIO Configurations

could you explain the open drain further? Thanks!

Re: PIO Configurations

A FET has a Gate input, and Drain-Source channel.

In an open-drain configuration, the drain is not connected to Vcc, ie open circuit. The Source is connected to ground via a resistor.

When there's no Vgs, the channel is switched off, and the output is pulled-to-low by the drain resistor.

When Vgs is present, the channel switches on, but no current flows as the drain is not connected. But it's not ground either due to the presence of the source resistor. What happens is that the output is now in a high impedence state. The output is determined by external factors! (ie it has become a passive input!)

In a push-pull configuration, the output can be pushed high and pulled low, hence its name. In an open-drain configuration, it can only be pulled low.

Re: PIO Configurations

I don't think it is the right comment.
Open drain (in MOS, CMOS....) is like open collector (in TTL, .....): drain is directly connected to the PIN and it will sink current to GND if any pull-up circuit (wheter resistor or anything else) is conneted to this pin. If active will maintain L (logic 0), if not active will allow H (logic 1). Used when there is possibility of connecting more then one open drain to the line (function: OR).

Example: I2C bus.