Forums

Problem regarding the Reset Pin of MCU

Started by Huey Fen September 24, 2005
Hi here. I am doing my final year project on the design of Single Board Computer by using M68HC11. But I am facing a problem on the reset pin of the M68HC11.
My reset circuitry worked fine without the connection of MCU. But once the MCU is connected to the reset circuitry, the reset pin (pin 17) of MCU became 0V. I suspected that the MCU had internally pull the reset pin to 0V. But I don't understand how could this be happened. At first, I suspected a failure with the MCU, hence I've replaced it with a new one. But the same problem occured.
So may I know what is the possible factor that can cause this phenomenon. Hopefully that you guys out there can give me some hints regarding this matter. Your help is greatly appreciated. Thanks in advance.

Best Regards,
circuitcyco

__________________________________________________




The reset pin of the 68hc11 is both an input and an output.

At 07:56 PM 9/24/2005 -0700, you wrote:
>Hi here. I am doing my final year project on the design of Single Board
>Computer by using M68HC11. But I am facing a problem on the reset pin of
>the M68HC11.
>My reset circuitry worked fine without the connection of MCU. But once the
>MCU is connected to the reset circuitry, the reset pin (pin 17) of MCU
>became 0V. I suspected that the MCU had internally pull the reset pin to
>0V. But I don't understand how could this be happened. At first, I
>suspected a failure with the MCU, hence I've replaced it with a new one.
>But the same problem occured.
>So may I know what is the possible factor that can cause this phenomenon.
>Hopefully that you guys out there can give me some hints regarding this
>matter. Your help is greatly appreciated. Thanks in advance.
>
>Best Regards,
>circuitcyco


There are a number of documents at the manufacturer's web site that may help
you (www.freescale.com <http://www.freescale.com>).
Some specific ones I found on a quick look include:
http://www.freescale.com/files/microcontrollers/doc/eng_bulletin/EB195.pdf

http://www.freescale.com/files/microcontrollers/doc/app_note/AN1744.pdf
and the largest link, section 5 from the 68HC11 reference manual is at

http://www.freescale.com/files/microcontrollers/doc/ref_manual/M68HC11RM.pdf

Darrell
On 9/24/05, Huey Fen <circuitcyco@circ...> wrote:
>
> Hi here. I am doing my final year project on the design of Single Board
> Computer by using M68HC11. But I am facing a problem on the reset pin of the
> M68HC11.
>




> Hi here. I am doing my final year project on the design of Single Board Computer by using M68HC11. But I am facing a problem on the reset pin of the M68HC11.
> My reset circuitry worked fine without the connection of MCU. But once the MCU is connected to the reset circuitry, the reset pin (pin 17) of MCU became 0V. I suspected that the MCU had internally pull the reset pin to 0V. But I don't understand how could this be happened. At first, I suspected a failure with the MCU, hence I've replaced it with a new one. But the same problem occured.
> So may I know what is the possible factor that can cause this phenomenon. Hopefully that you guys out there can give me some hints regarding this matter. Your help is greatly appreciated. Thanks in advance.

HC11 pulls internally reset line low, but for a short time.
What's your external reset circuitry ? Maybe something is wrong here ?
Show us the schematic or at least describe it.

--
Michal Konieczny
mk@mk@....



Huey Fen wrote:
> Hi here. I am doing my final year project on the design of Single Board Computer by using M68HC11. But I am facing a problem on the reset pin of the M68HC11.
> My reset circuitry worked fine without the connection of MCU. But once the MCU is connected to the reset circuitry, the reset pin (pin 17) of MCU became 0V. I suspected that the MCU had internally pull the reset pin to 0V. But I don't understand how could this be happened. At first, I suspected a failure with the MCU, hence I've replaced it with a new one. But the same problem occured.
> So may I know what is the possible factor that can cause this phenomenon. Hopefully that you guys out there can give me some hints regarding this matter. Your help is greatly appreciated. Thanks in advance.
>

Please hit return from time to time, ok?

The /RESET pin in an input and an output. There are several possible
causes for what you describe. Put up a description of your circuit
and maybe we can help. Do you have COP enabled?

Mike
--
p="p=%c%s%c;main(){printf(p,34,p,34);}";main(){printf(p,34,p,34);}
This message made from 100% recycled bits.
You have found the bank of Larn.
I can explain it for you, but I can't understand it for you.
I speak only for myself, and I am unanimous in that!



With this, i attach the schematic of my design for your reference.
The reset circuitry should be okie. Because if MCU is disconnected from it, I would obtain 5V when the reset button is released and 0V when reset button is pressed. As you can see from the schematic as well, I am trying to use a PSD to expand the memory space of my design. If PSD reset pin is the connected to the reset circutry without MCU, then I would still get the correct reading at reset pin of PSD. But once MCU is connected to reset circuitry, everything goes wrong. I suspect the MCU had internally pull the reset pin low. But I don't understand how could this happen. I came across a sentence stated that reset pin of MCU will give an open drain output to indicate internal failure from M68HC11 reference manual. Is it the case that I am facing now? Any solution for that?
I've been tried to operate the MCU in special bootstrap mode. But I was failed to get the MCU communicate with the host PC. Will the CONFIG of MCU been modified during the bootstrap mode? (But I didn't get the MCU successfully communicate with PC) I didn't do any configuration on the MCU. But the PSD is configured. So I am not sure the COP is being enable or not. I am still trying to figure out this.
Hopefully that I can get your reply soon. Your help is much appreciated. Thanks a lot. Huey Fen wrote:
> Hi here. I am doing my final year project on the design of Single Board Computer by using M68HC11. But I am facing a problem on the reset pin of the M68HC11.
> My reset circuitry worked fine without the connection of MCU. But once the MCU is connected to the reset circuitry, the reset pin (pin 17) of MCU became 0V. I suspected that the MCU had internally pull the reset pin to 0V. But I don't understand how could this be happened. At first, I suspected a failure with the MCU, hence I've replaced it with a new one. But the same problem occured.
> So may I know what is the possible factor that can cause this phenomenon. Hopefully that you guys out there can give me some hints regarding this matter. Your help is greatly appreciated. Thanks in advance.
>

Please hit return from time to time, ok?

The /RESET pin in an input and an output. There are several possible
causes for what you describe. Put up a description of your circuit
and maybe we can help. Do you have COP enabled?

Mike
--
p="p=%c%s%c;main(){printf(p,34,p,34);}";main(){printf(p,34,p,34);}
This message made from 100% recycled bits.
You have found the bank of Larn.
I can explain it for you, but I can't understand it for you.
I speak only for myself, and I am unanimous in that! SPONSORED LINKS
Freescale semiconductor inc Microcontrollers Pic microcontrollers 8051 microprocessor

---------------------------------
YAHOO! GROUPS LINKS --------------------------------- ---------------------------------
Yahoo! for Good
Click here to donate to the Hurricane Katrina relief effort.



> With this, i attach the schematic of my design for your reference.

This list doesn't accept attachments. Please publish somewhere and give
us URL.

--
Michal Konieczny
mk@mk@....



Huey Fen wrote:
> With this, i attach the schematic of my design for your reference.

Sorry, they get stripped. Either include ASCII art, or verbal
description, or give us a URL.

> The reset circuitry should be okie. Because if MCU is disconnected
from it, I would obtain 5V when the reset button is released and 0V when
reset button is pressed. As you can see from the schematic as well, I am
trying to use a PSD to expand the memory space of my design. If PSD
reset pin is the connected to the reset circutry without MCU, then I
would still get the correct reading at reset pin of PSD. But once MCU is
connected to reset circuitry, everything goes wrong. I suspect the MCU
had internally pull the reset pin low. But I don't understand how could
this happen. I came across a sentence stated that reset pin of MCU will
give an open drain output to indicate internal failure from M68HC11
reference manual. Is it the case that I am facing now? Any solution for
that?
> I've been tried to operate the MCU in special bootstrap mode. But I
was failed to get the MCU communicate with the host PC. Will the CONFIG
of MCU been modified during the bootstrap mode? (But I didn't get the
MCU successfully communicate with PC) I didn't do any configuration on
the MCU. But the PSD is configured. So I am not sure the COP is being
enable or not. I am still trying to figure out this.
> Hopefully that I can get your reply soon. Your help is much
appreciated. Thanks a lot.

Still haven't found the RETURN key, I see.

As I stated, the /RESET pin is both an input and an output. I didn't
ask about COP with idle curiosity. It is a common mistake to get COP
resets. Any internal reset cause will force the /RESET pin low (active).
There may be an interaction which causes your external circuit
to latch up when this occurs.

[snip inclusion]

Mike
--
p="p=%c%s%c;main(){printf(p,34,p,34);}";main(){printf(p,34,p,34);}
This message made from 100% recycled bits.
You have found the bank of Larn.
I can explain it for you, but I can't understand it for you.
I speak only for myself, and I am unanimous in that!



I didn't realize that the schematic was stripped. I've upload the schematic to m68hc11 yahoo! groups photo album.u guys may view from there.sorry for the inconvenience.

>Still haven't found the RETURN key, I see.

I do not really understand what do you mean with RETURN key. Can you explain more on this?

Thank you. ---------------------------------
Yahoo! for Good
Click here to donate to the Hurricane Katrina relief effort.



> I didn't realize that the schematic was stripped. I've upload the schematic to m68hc11 yahoo! groups photo album.u guys may view from there.sorry for the inconvenience.

Give us URL, please

> >Still haven't found the RETURN key, I see.
>
> I do not really understand what do you mean with RETURN key. Can you explain more on this?

Every "paragraph" of your mail is one single looong line of text, just
hard to read when one has to scroll horizontally.
Please write your mail so that every line (not paragraph) has "hard"
return at the end, and is no longer than 70-80 chars.

--
Michal Konieczny
mk@mk@....