Main Site Documentation

What does this mean: Pull the RX pin high on the first sensor for at least 20uS


Hi electronics People…I know you may go like “…so what the heck are you here for… if you have no electrical background?”

Anyway, what the heck does it mean by: Pull the RX pin high for at least 20uS?

Could someone translate that into action items that someone with no electrical experience would understand? :smiley:

Also 20uS (microsecond) seems to be very small as (1 millisecond = 1000 microseconds) does that seem reasonable or it is by mistake, basically diasy chaining the sensors is what I am trying to do here.

Appreciate it!


From a SW point of view: pull HI == set pin to true (1). You are ‘pulling up’ the signal to Vcc.


From a HardWare point of view: pull the RX wire at least 20" up :smiley: Just hope you have a very fast arm, because 20uS … is very very very fast


low = pin set to false, high = pin set to true.

Think of a Square Wave (like a PWM trace || || |_|) voltage is at the top, ground is at the bottom. If you’re pulling something UP/High, your taking it towards the voltage. If you’re pulling something DOWN/Low you’re taking it to ground.

20uS is a really long time for something like a 30MHz dsPIC or just a raw NXP Arm7 like the domino runs on. A dsPIC33F can toggle a pin in 0.0007 miliseconds, an M3 Coretex is about the same. An ARM 7 should be able to do it in 1/3rd of that time.


lol yes, 20uS is a LONG time when it comes to modern processor.

Think about it this way, FEZ is 72Mhz, that is 72 million instructions per second, or an instruction every 0.014us :smiley: … or 71 instructions every 1uS … how do you like that? :smiley:


Thanks Guys for very quick answers,

I think the easiest answer to understand is from EriSan500, that I may be able to.

Thanks All!