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.

Reply to
Tomás Ó hÉilidhe
Loading thread data ...

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

Reply to
Mike Silva

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?

Reply to
Hans-Bernhard Bröker

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.

Reply to
Tomás Ó hÉilidhe

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

Reply to
Rocky

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:

formatting link

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.

Reply to
Tomás Ó hÉilidhe

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.

Reply to
Dombo

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

Reply to
Rocky

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

Reply to
Tomás Ó hÉilidhe

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

Reply to
Tomás Ó hÉilidhe

Put half an amp through your LEDs without current limiting resistors and you may create one ;->

Reply to
s0lstice

Actually, I would expect that to produce a sound instead. As in: PING and they're gone.

Reply to
Hans-Bernhard Bröker

It might not be the LED that goes.

Reply to
s0lstice

Reminds me of the original IBM monochrome display for the PC. Set a wrong time or rep rate in the bios and the display cooks the horizontal (I think) drive transistor.

--
 [mail]: Chuck F (cbfalconer at maineline dot net) 
 [page]: 
 Click to see the full signature
Reply to
CBFalconer

Been there, done that. Some of the registers in the original mono display controller card were write-only. Any accesses to those register's addresses were handled as writes. If you tried to read them, you ended up writing unkown values. I attempted to read the wrong set of I/O addresses using debug, and I let the smoke out of one of the high-voltage sections of the display.

--
Grant Edwards                   grante             Yow! Gee, I feel kind of
                                  at               LIGHT in the head now,
 Click to see the full signature
Reply to
Grant Edwards

ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.