Each GPIO pin runs at +3.3V and can safely source 16mA. Combined, they can source 50mA. There is no over-voltage protection on the pins, and they are not current limited, so be sure to test any connections with a voltmeter before making them.
The 5V rail can source as much amperage as is provided by the power supply minus that used by other peripherals and the Pi itself. Be mindful about overdrawing it, though, as underpowering the Pi causes it to skip cycles and ultimately crash.
Because the logic is obviously never going to be perfectly 0V = Low, 3.3V = High, the transition is determined by the maximum Low and the minimum High voltages:
- Maximum Low Voltage: 0.8V
- Minimum High Voltage: 1.3V
So there is some hysteresis, when the voltage drops below 0.8V it will register as Low, and will continue to read Low only until it reaches higher than 1.3V.
- Raspberry Pi gpio via mmap - an example of directly writing to the GPIO pins with mmap. This is how pigpio interacts with gpio pins