Slew rate is when signal may be slow in changingChristoph1985 wrote:Hello,
can somebody please explain, what slew and hysteresis are for?
These are parameters you can find in the eeprom settings.
In which cases will I need this settings?
gpio_drive sets the maximal current for all usable GPIO pins? (for ex. 16 mA per pin?)
Thanks in advance
Fun anecdote time: logic (CMOS) inputs without hysteresis act as quite high-gain RF amplifiers if you let their inputs wander to VDD/2. On a particularly ancient and badly-designed board that I had the displeasure of repairing quite a few times, leakage currents and a dodgy terminal connection conspired to make a 4000 series hex inverter bounce up and down at about 18MHz. The output traces were coupling to the input traces at that frequency.Burngate wrote:Hysteresis (for a digital input): a change from 0 to 1 occurs at a higher input voltage than a change from 1 to 0. There's never an input voltage that's undetermined.
Without hysteresis, there can be an input voltage that may produce either 0 or 1
Slew rate (for an output): in the real world it takes time for a pin to change from one state to another. In between, it's neither one nor t'other.
Because all real circuits have capacitance (and inductance, resistance, etc.) and to change a pin's voltage requires the capacitance to charge, large currents can flow.
Among other things, that can cause interference on adjacent wires. Limiting the rate at which the voltage changes reduces those problems, at the expense of more time before it's valid.