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[SOLVED] I need a a-fixed-value-device ?

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henninggs

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I have 4 PCB's with a microcontroller on each. The boards are identically in both hardware and software.
Now when powered on I would like MCU A to run subroutine A, MCU B to run subroutine B and so on. - so I need a way to tell each MCU what to run.

This could be done with at dip switch and a shift register or I could read the value of a resistor. A voltage drop of 0.5v could mean subroutine A, a voltage drop of 1v subroutine B and so on, but this would require that the MCU has a ADC.

If I had a register with a fixed factory-stored value that behaved like a shift register the MCU could just clock the number/value out at start up.
Does such a device exists ? (Need something around 8 bit)

Thanks for any replies.
Regards
 
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skogsjanne

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An easy way to do it without an ADC is to measure the charge/discharge time for an RC-link.
 

henninggs

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Ah that's smart. What is a RC-link exactly ? (I assume it involves a Resistor and a Capacitate)
 

skogsjanne

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R between VDD and pin and C between pin and GND. For example. Or the other way round (not so common).

Set pin to output, pull low to discharge C, set pin to input, measure time for input to change from 0 to 1. Not very exact but good enough to differentiate between four different versions. Or eight. Or maybe sixteen. Maybe not.
 

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