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active low or active high?

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neroburn

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active low active high

I wonder which one is better for designing using MCU? AL or AH? any comment
 

what is an active low output

Ordinarily the choice is based on the application needs. Such question will arise only if there is a critical demanding consideration on resources. If such a situation is there, if tabled, may help one to think along those lines to come up with plasible suggestions.
Regards
Raoof
 

active low, active high

It is very common to implement a pullup resistor, then attach sinking logic. This would imply active low. You'll also find some logic that is active on one clock phase, while other logic is inactive. By mixing your active signals you can often reduce hardware.

You will find that most digital logic sinks as opposed to sources. Yet in industrial PLC applications you'll find predominately sourcing logic.
 

active high

It will be usually less resource taxing on the microcontroller doing
a active low output.
Current is pull from outside the IC into the IC.
Active high output, take the supply from the IC.

Best Regards,
Siong Boon

MODERATOR - SIGNATURE LINKS ARE NOT ALLOWED
 

active high active low

It depends with the current rating of the MCU. IF AL current is higher than AH then design the load to activate it in active low.
 

active low

I always use active low but not for the reasons already given.

Low always means zero volts or close to it. On a system with multiple supply rails, a high could be any one of them and may not be universally recognized, even within a single circuit.

For example, one of my designs uses 5V LCD modules and 2.5V microprocessors. A low is the same for both of them but a high from the microprocessor is still a low as far as the LCD is concerned.

I don't think arguments based on supplying or sinking current are valid. Most ICs have symetrical output stages and their current ratings are roughly the same whichever way it flows.

Brian.
 

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