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pins state at start-up

 
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knight



Joined: 23 Oct 2012
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pins state at start-up
PostPosted: Tue Oct 23, 2012 1:47 am     Reply with quote
hi,
I want to ask about the pins state at start-up. Are they High or Low?
I want to connect a relay with microcontroller using transistor (port B and C).
Currently I am using pic16f870. Can anyone tell me about the pins (port) state at start-up?
Mike Walne



Joined: 19 Feb 2004
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PostPosted: Tue Oct 23, 2012 2:37 am     Reply with quote
Quote:
I want to ask about the pins state at start-up. Are they High or Low?
Neither.

It's all in the data sheets.

Generally speaking pins states are INPUT on reset or powerup.

Therefore float if unattached.

If it's important they are in particular state, then it's usual to pull either up or down with a suitable resistor.

Mike
rikotech8



Joined: 10 Dec 2011
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PostPosted: Tue Oct 23, 2012 10:24 am     Reply with quote
How becomes writing into a certain port. Is it like this: read-modify_data-write?
Mike Walne



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PostPosted: Tue Oct 23, 2012 10:35 am     Reply with quote
Quote:
How becomes writing into a certain port. Is it like this: read-modify_data-write?
I don't understand the question.

Please try again.

Mike
asmallri



Joined: 12 Aug 2004
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PostPosted: Wed Oct 24, 2012 8:33 am     Reply with quote
rikotech8 wrote:
How becomes writing into a certain port. Is it like this: read-modify_data-write?


Yes BUT if you are using a PIC18F or higher family then you would write to the LAT register and not the PORT. This solves the read-modify-write problem for a pin that is heavily loaded.
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