AVR-Chat

Hmmhm, discussion seems to have strayed a bit, but just in case 
anyone ever runs across the same problem:

* I definately had the pins on the AVRs configured as outputs. 

* The same fault occured with both 74HC and 74LS chips, but only on   
   my newer batches of Mega16s and Tiny26s.

* In both cases, the problem was cured by fitting external 100k    
  pulldown resistors. NO CODE CHANGES.

* I know it sounds like I had the pins configured as inputs and using 
  the internal pullup to pull it high, but thats just not the case.

Cheers
Hein B


--- In AVR-Chat@yahoogroups.com, "James Hatley" <james.hatley@...> 
wrote:
>
> Yes, Jose, good point on pull ups. I forgot about them as I never 
use them
> here. I disable them globally. Old habits from using Motorola 
processors and
> if pull ups are needed I put the specific one required external to 
the
> processor.
> 
> Good luck with your project.
> 
> Jim
> 
> ----- Original Message ----- 
> From: "Jose Fuentes" <josecarlosfuentes@...>
> To: <AVR-Chat@yahoogroups.com>
> Sent: Monday, April 03, 2006 11:57 AM
> Subject: Re: [AVR-Chat] Connecting AVRs directly to inputs of 74HC 
and LS
> logic chips.
> 
> 
> > --- James Hatley <james.hatley@...> 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@...>
> > > 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.
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> > > -------------------------------------------------
> > > > > Dennis Clark          TTT Enterprises
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