AVR-Chat

--- James Hatley <james.hatley@comcast.net> escribió:

> Jose,
> 
> All Atmel processors (as far as I know anyway) have
> three registers for a
> port, one is for setting the output bits that you
> have declared output
> (PORTA), one is for reading the input bits you
> declared input (PINA) and of
> course, the DDRA register for setting which bits are
> input and which are
> output.

But it doesn't mean you can not write on the
corresponding register PORTx of an input pin.  When
you configure a pin as input, and write a "0" to it
(by writing PORTx register) the pin enters in high-Z
state, if you write a "1" to it and PUD bit is set,
then pin is pulled-up.

Also you can read PORTx registers because they are
read/write registers.

> Register PINA is used when you want to read the
> input of the port or just
> read a bit in the register. It reflects the input to
> PORTA.

You are right, PINA is a read-only register.
 
> Register PORTA is used when you what to set bits of
> the port or just set a
> bit. If you read PORTA it is reading what is
> programmed in to the output
> register for PORTA.
> 
> It all depends on how you have set DDRA, inputs or
> outputs as to what
> register you use and what you want to do with the
> bit.
> 
> To set a bit with the bit declared output high use
> PORTA=PORTA|0x01;, to use
> your example. Or to set it low use PORTA=PORTA&0xfe;
> ( Most use macros here
> to manipulate bits as it is much more fool proof. )
> 
> To read a bit with the bit declared input use
> FOO=PINA&0xfe, to use your
> example.
> 
> Maybe this is too simplified but hope it helps some,
> 
> Jim
> 
> 
> 
> 
> ----- Original Message ----- 
> From: "Jose Fuentes"
> <josecarlosfuentes@yahoo.com.ar>
> To: <AVR-Chat@yahoogroups.com>
> Sent: Sunday, April 02, 2006 11:39 PM
> Subject: Re: [AVR-Chat] Connecting AVRs directly to
> inputs of 74HC and LS
> logic chips.
> 
> 
> > I have a board with an AVR driving a LS chip
> directly,
> > and it works fine.  But I had problems with source
> > code like this:
> >   PORTA = PINA | 0x01;
> > It seems that under certain conditions PORTA is
> not
> > equal to PINA.  I modified the code like this:
> >   PORTA = PORTA | 0x01;
> > and it solved the problem.
> >
> > The first thing that comes to mind when you say
> that
> > "AVR was unable to pull the input on the logic
> chip
> > completely low" is that AVR pin was actually set
> as
> > input.  That way you would be pulling high the pin
> by
> > using the internal pull-up.  But you woudn't be
> able
> > to pull down the pin because it just would enter
> into
> > high impedance state.
> >
> >
> >
> >
> > Regards
> >
> > Jose
> >
> >
> >
> > > kernels_nz wrote:
> > > > Hi Guys,
> > > >
> > > > Ive had two different boards lately give a lot
> of
> > > trouble, both had
> > > > OUTPUTS on AVR chips connected directly to
> inputs
> > > on 74HC and 74LS
> > > > logic chips.
> > > >
> > > > Looking at it with my scope, it appeared that
> the
> > > AVR was unable to
> > > > pull the input on the logic chip completely
> low ?
> > > It would pull it to
> > > > around 1 to 3 volts for a low output.
> > > >
> > > > I did ensure that the pins were set up as
> OUTPUTS,
> > > nothing else
> > > > weird.
> > > >
> > > > Both problems were solved by connecting 100k
> > > resistors from the input
> > > > pins on the logic chips to ground.
> > > >
> > > > Any ideas ? Im sure it will be obvious as soon
> as
> > > someone points out
> > > > the obvious, but it's got me beat.
> > > >
> > > > Cheers
> > > > Hein B
> > > > Andante Technology
> > > > Auckland
> > > > New Zealand.
> > > >
> > > >
> > > >
> > > >
> > > >
> > > >
> > > >
> > > >
> > > >
> > > >
> > > > Yahoo! Groups Links
> > > >
> > > >
> > > >
> > > >
> > > >
> > > >
> > >
> > > -- 
> > >
> -------------------------------------------------
> > > Dennis Clark          TTT Enterprises
> > > www.techtoystoday.com
> > >
> -------------------------------------------------
> > >
> > >
> > >
> > > Yahoo! Groups Links
> > >
> > >
> > >     AVR-Chat-unsubscribe@yahoogroups.com
> > >
> > >
> > >
> > >
> > >
> >
> >
> > __________________________________________________
> > Correo Yahoo!
> > Espacio para todos tus mensajes, antivirus y
> antispam ¡gratis!
> > ¡Abrí tu cuenta ya! - http://correo.yahoo.com.ar
> >
> >
> >
> > Yahoo! Groups Links
> >
> >
> >
> >
> >
> >
> >
> 
> 
> 
> 
>  
> Yahoo! Groups Links
> 
> 
>     AVR-Chat-unsubscribe@yahoogroups.com
> 
>  
> 
> 
> 


__________________________________________________
Correo Yahoo!
Espacio para todos tus mensajes, antivirus y antispam ¡gratis! 
¡Abrí tu cuenta ya! - http://correo.yahoo.com.ar