I've highlighted this symbol from page 30 of the TMC2100 datasheet:
Based on the context, which says "only rising edges are active", I'm guessing it means that a signal is detected when the input voltage rises from 0.44×VCC_IO to 0.56×VCC_IO within a given period of time (e.g. from 2.2V to 2.8V if VCC_IO is 5V).
Is that correct, or does it have a different meaning?
Does anyone have a link to a cheat sheet that contains this symbol?
It is the symbol for hysteresis, which the Schmitt Trigger is implementing. The symbol is a stylized graph of the input voltage on the x-axis and the output voltage on the y-axis. The output will transition from low to high at 0.56 x VCCio and will transition from high to low at 0.44 x VCCio. This "cleans up" slow or noisy input signals and prevents spurious high frequency transitions around the logic threshold. See also: https://www.ti.com/lit/an/scea046a/scea046a.pdf?ts=1674683984329
The symbol represents just what you would see on an oscilloscope in X-Y mode with input voltage on the X axis and output voltage on the Y axis, and a relatively (compared to the switching times) very slow ramp or sawtooth waveform applied (a sine wave would work too but on an analog oscilloscope the traces would be fatter at the ends). Image from here.
In this case Vtl is 0.44*Vdio and Vth is 0.56*Vddio, so 2.2V and 2.8V in your example, and Vhst is the difference of 0.12*Vddio or 0.6V in your example.
This is like the mechanical over-center snap action of a switch, it prevents the output from responding to small variations in the input and makes the output transition times short regardless of how slowly the input changes.
I think if you understand the origin of the hysteresis symbol you won't ever need a cheat sheet to remember what it means.
