Suppose we have an SPI output, it is sourcing a standard logic level (say 3.3 V). Suppose the output is connected to a trace on a PCB with impedance 50 Ohms, and the signal is going to a capacitive load (another integrated circuit). Suppose we know the current associated with that logic level.
If I were to instead make my trace 40 Ohms and change nothing else, will the output current in that logic level change? Ohm's law says yes, it would increase.
However, because push-pull buffers have their own source impedance that depends on their driving signal, I do not know if this change in output current would actually happen. If the current stayed constant when the line impedance were dropped to 40 Ohms, that would mean the buffer's output impedance had to increase by 10 Ohms.
So what would happen in this hypothetical situation?
EDIT: I am not referring to the DC state when the signal has settled at its voltage level. To charge up the CMOS input, there has to be some current flow on the line until that charge up is completed. I'm trying to understand what is this current.
EDIT2: Let's just ignore things like reflections etc., just want to know how the driving circuit forms its output voltage and current, and how do those quantities propagate along the trace until they eventually reach the load.