Just assume that it's not in a defined state?

You know chips like the 164 shift register, well I've been reading
over the data sheet and it doesn't mention anything about the "boot
up" state of the device. That is to say, if I have the master-reset
tied high (it's active low), then what happens when I apply power?
Will it start off all zeroes, or will it be in an indeterminate state?

Similary I'm trying to find this information for the 4017 counter
decoder chip.

The reason I want to know is that I'm hoping to get rid of RC circuits
if I don't need them.

On May 4, 12:04=A0pm, Tom=E1s =D3 h=C9ilidhe <t...@lavabit.com> wrote:
> You know chips like the 164 shift register, well I've been reading
> over the data sheet and it doesn't mention anything about the "boot
> up" state of the device. That is to say, if I have the master-reset
> tied high (it's active low), then what happens when I apply power?
> Will it start off all zeroes, or will it be in an indeterminate state?
>
> Similary I'm trying to find this information for the 4017 counter
> decoder chip.
>
> The reason I want to know is that I'm hoping to get rid of RC circuits
> if I don't need them.

If the datasheet doesn't explicitly guarantee something (power-up
state in this case), you can't make any assumptions about it.
Certainly, if a chip has a reset input and you choose not to use it,
don't expect any reset-like action anyway.

If you have an extra IO pin on your uC you can use it and a pulldown
resistor (since the '164 reset is active low) to force the '164 to
power up in a reset state until your code turns the uC pin to an
output and drives the reset line inactive (high).  Of course, if you
have hardware that generates a powerup reset signal external to the uC
you can use that as well.

Mike

Tom�s � h�ilidhe wrote:

> That is to say, if I have the master-reset
> tied high (it's active low), then what happens when I apply power?

Wrong question.  The right question is: should you tie that pin high? 
The answers is: no you shouldn't do that.

Why do you think the device has a reset pin in the first place: just to 
tease engineers?

On May 4, 6:44=A0pm, Hans-Bernhard Br=F6ker <HBBroe...@t-online.de> wrote:
> Tom=E1s =D3 h=C9ilidhe wrote:
> > That is to say, if I have the master-reset
> > tied high (it's active low), then what happens when I apply power?
>
> Wrong question. =A0The right question is: should you tie that pin high?
> The answers is: no you shouldn't do that.
>
> Why do you think the device has a reset pin in the first place: just to
> tease engineers?


Even if the chip starts up as all zeroes, there still might be a
reason to reset it to all zeroes after you've been playing with it for
a while.

On May 4, 6:04=A0pm, Tom=E1s =D3 h=C9ilidhe <t...@lavabit.com> wrote:
> You know chips like the 164 shift register, well I've been reading
> over the data sheet and it doesn't mention anything about the "boot
> up" state of the device. That is to say, if I have the master-reset
> tied high (it's active low), then what happens when I apply power?
> Will it start off all zeroes, or will it be in an indeterminate state?
>
> Similary I'm trying to find this information for the 4017 counter
> decoder chip.
>
> The reason I want to know is that I'm hoping to get rid of RC circuits
> if I don't need them.

Just out of curiosity - what are the other pins on the PIC being used
for?
Rocky

> Just out of curiosity - what are the other pins on the PIC being used
> for?

I've 12 pins available altogether:

* 7 are going to LED's.
* 1 is clocking a counter.
* 3 are taking input from buttons.
* 1 is turning a piezo speaker on and off.

Here's my current schematic:

http://freepdfhosting.com/uploads/c01e0f0837.pdf

It has NPN transistors where it should have PNP because I've just
recently changed the chips I'm using. I plan on replacing the bi-polar
transistors with MOSFET's, just as soon as I figure out which ones are
suitable. I need one that can pass 500 mA, and another that can pass 2
A.

Tom�s � h�ilidhe schreef:
>> Just out of curiosity - what are the other pins on the PIC being used
>> for?
> 
> I've 12 pins available altogether:
> 
> * 7 are going to LED's.
> * 1 is clocking a counter.
> * 3 are taking input from buttons.
> * 1 is turning a piezo speaker on and off.
> 
> Here's my current schematic:
> 
> http://freepdfhosting.com/uploads/c01e0f0837.pdf
> 
> It has NPN transistors where it should have PNP because I've just
> recently changed the chips I'm using. I plan on replacing the bi-polar
> transistors with MOSFET's, just as soon as I figure out which ones are
> suitable. I need one that can pass 500 mA, and another that can pass 2
> A.

You could save two I/O pins if connect the input buttons to a voltage 
divider network on one side and the other side of the buttons to an 
analog input of your uC.

On May 4, 8:53=A0pm, Tom=E1s =D3 h=C9ilidhe <t...@lavabit.com> wrote:
> > Just out of curiosity - what are the other pins on the PIC being used
> > for?
>
> I've 12 pins available altogether:
>
> * 7 are going to LED's.
> * 1 is clocking a counter.
> * 3 are taking input from buttons.
> * 1 is turning a piezo speaker on and off.
>
> Here's my current schematic:
>
> http://freepdfhosting.com/uploads/c01e0f0837.pdf
>
> It has NPN transistors where it should have PNP because I've just
> recently changed the chips I'm using. I plan on replacing the bi-polar
> transistors with MOSFET's, just as soon as I figure out which ones are
> suitable. I need one that can pass 500 mA, and another that can pass 2
> A.

Thanks - It explains the pre-occupation with wanting 1 pin to drive
the counter/shiftregister. I think there better ways of handling the
problem, but I'm off to bed now.
Rocky

On May 4, 8:27=A0pm, Dombo <do...@disposable.invalid> wrote:

> You could save two I/O pins if connect the input buttons to a voltage
> divider network on one side and the other side of the buttons to an
> analog input of your uC.


Thanks for pointing that out, it hadn't crossed my mind. I'm looking
into it.

Now I just need to find something frivolous to do with two extra
pins :-D  Any ideas? I've already got seven segment displays and a
piezo speaker. What else can I put on it? It's a shame they don't have
chips that can give out a smell :P

On May 4, 9:38=A0pm, Tom=E1s =D3 h=C9ilidhe <t...@lavabit.com> wrote:
> On May 4, 8:27=A0pm, Dombo <do...@disposable.invalid> wrote:
>
> > You could save two I/O pins if connect the input buttons to a voltage
> > divider network on one side and the other side of the buttons to an
> > analog input of your uC.
>
> Thanks for pointing that out, it hadn't crossed my mind. I'm looking
> into it.


Actually do you think it would be worth the hassle having to deal with
the user pressing more than one button simultaneously?