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


#1


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!


#2

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


#3

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


#4

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.


#5

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:


#6

Thanks Guys for very quick answers,

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

Thanks All!


#7

:wink: