Just assume that it's not in a defined state?
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From: Mike Silva on 4 May 2008 13:28 On May 4, 12:04 pm, Tomás Ó hÉilidhe <t...(a)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
From: Hans-Bernhard Bröker on 4 May 2008 13:44 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?
From: Tomás Ó hÉilidhe on 4 May 2008 14:01 On May 4, 6:44 pm, Hans-Bernhard Bröker <HBBroe...(a)t-online.de> wrote: > Tomás Ó hÉilidhe 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? 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.
From: Rocky on 4 May 2008 14:30 On May 4, 6:04 pm, Tomás Ó hÉilidhe <t...(a)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
From: Tomás Ó hÉilidhe on 4 May 2008 14:53
> 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. |