PLEASE REMOVE IT_5

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#1
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Hi,

 

What's the problem??

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Last Edited: Wed. Mar 14, 2018 - 06:13 AM
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mvtdesign wrote:

What's the problem??

 

There is no problem, those levels are perfectly within spec.

 

It's more normal to connect LEDs so that a '0' on the IO pins turns them on by having one side of the LED connected to +ve and the other, via the resistor, to the IO pin.

#1 Hardware Problem? https://www.avrfreaks.net/forum/...

#2 Hardware Problem? Read AVR042.

#3 All grounds are not created equal

#4 Have you proved your chip is running at xxMHz?

#5 "If you think you need floating point to solve the problem then you don't understand the problem. If you really do need floating point then you have a problem you do not understand."

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What does the datasheet say?

Note that the electrical characteristics of PC6 differ from those of the other pins of Port C.
 

I recall threads with previous discussions on this.  The datasheet doesn't have any numbers on this "differing" that I can see.

You can put lipstick on a pig, but it is still a pig.

I've never met a pig I didn't like, as long as you have some salt and pepper.

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You mean it's ok??

 

Last Edited: Wed. Mar 14, 2018 - 06:03 AM
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Yeah, I couldn't find the characteristics of this pin, Just I can see the characteristics of RESET#

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Sorry, just to be clear - you have activated the RSTDISBL fuse? If so how are you programming the mega8? I assume an STK500 and using HVPP?

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theusch wrote:

The datasheet doesn't have any numbers on this "differing" that I can see.

 

There's a couple of graphs from which you can infer how different they are.

#1 Hardware Problem? https://www.avrfreaks.net/forum/...

#2 Hardware Problem? Read AVR042.

#3 All grounds are not created equal

#4 Have you proved your chip is running at xxMHz?

#5 "If you think you need floating point to solve the problem then you don't understand the problem. If you really do need floating point then you have a problem you do not understand."

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From another AVR datasheet:

The reset pin can also be used as a (weak) I/O pin.
 

 

And also remember there are no protection diodes.

 

6. The RESET pin must tolerate high voltages when entering and operating in programming modes and, as a consequence,
has a weak drive strength as compared to regular I/O pins. See Figure 21-24, Figure 21-25, Figure 21-26, and Figure 21-27
(starting on page 198)
 

Compare the drive chart with "normal" pins:

You can put lipstick on a pig, but it is still a pig.

I've never met a pig I didn't like, as long as you have some salt and pepper.

Last Edited: Fri. Oct 28, 2016 - 05:09 PM
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I'm using a programmer which I've bought a few days ago...

Last Edited: Wed. Mar 14, 2018 - 06:05 AM
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Wow, I remember in ATtiny13A, the reset output (PB5) was exactly like other pins.

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mvtdesign wrote:
Wow, I remember in ATtiny13A, the reset output (PB5) was exactly like other pins.

Let's explore that a bit...

You can put lipstick on a pig, but it is still a pig.

I've never met a pig I didn't like, as long as you have some salt and pepper.

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Unless you are using tons of chips, and using the Reset\ as a general purpose I/O pin saves you from stepping up to a larger uC and a higher cost, it would generally seem reasonable to use a uC with enough pins such that one didn't have to mess with the Reset\  pin.

 

Have you been successful in HVPP'ing the chip after locking yourself out of normal programming via programming the Reset\ pin to be a general purpose I/O?

 

I wasn't aware that one could HVPP the uC with a Centronics PP interface programmer.

 

If you post a schematic of your project you get a suggestion or two that could save you needing to use the Reset\ pin.

 

JC

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Thank you, good luck :)

Last Edited: Wed. Mar 14, 2018 - 06:07 AM
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I have no schematics

Last Edited: Wed. Mar 14, 2018 - 06:09 AM
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mvtdesign wrote:
Yeah, exactly, I didn't want to waste PC6, the IO works and my programmer works too, but the output of PC6 is too weak and maybe it's more useful as input (like PIC microControllers). And I have no schematics at the moment, because I'm working on a bread board.

Interesting.  I guess "suit yourself".  We have many scores of production AVR8 designs, and all are ISPed.  When you have a real board and need to update the firmware, do you unsolder the micro from every unit to isolate from app circuitry that will not tolerate 12V?  And then resolder it onto each unit?

 

Moving the micro every iteration, even with ZIF sockets, gets onerous very quickly even with a single dev unit on the bench.

You can put lipstick on a pig, but it is still a pig.

I've never met a pig I didn't like, as long as you have some salt and pepper.

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Thanks for your help :)

Last Edited: Wed. Mar 14, 2018 - 06:12 AM
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mvtdesign wrote:

You mean it's ok??

 

So I'll connect the LED cathode to the PC6, and the LED anode to Vcc and will turn it on with 0 instead 1.

 

Ok, Thanks :)

 

So are you using a current setting series resistor with your LED?

 

Ross McKenzie, Melbourne Australia

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Yes, a 470 Ohm.

Last Edited: Sat. Oct 29, 2016 - 04:34 AM
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So, after having determined that you really want to use the Reset\ pin, (which many think is just not worth the added effort...), the next question is:

 

What else is the uC connected to?

 

Obviously one might consider putting the LED on a "real" I/O pin, and using the Reset\ pin as a digital signal where it doesn't have to drive a load, (use it as either an input or an output with a significant load, eg driving another chip, etc.).

 

JC

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PLEASE REMOVE THIS THREAD

Last Edited: Wed. Mar 14, 2018 - 06:13 AM