LPC1227 GPIO pins Reset Value Causing Problems

[lpcware]

Content originally posted in LPCWare by th_shak on Mon Jan 28 13:18:29 MST 2013
Hello,
According to the datasheet of LPC1227 all IO pins are set to digital mode with pull-ups enabled at reset. This causes very serious problems. If we have some leds connected to GPIO pins they will light at reset, or even worst, if we have a step-up circuit connected directly to a GPIO pin it will "fry" since we are in reset, it will go high and without any control from the software the produced voltage will climb to "thousands" of volts. What is this silly mistake you have done and how we can overcome it without connecting external pull-down resistors to the "critical" pins? You could set the reset value to Open Drain mode! :mad:(These are not theoretical assumptions, but facts that I have tested and I'm 100% sure that are happening exactly as I'm saying).

Thank's

[lpcware]

Content originally posted in LPCWare by MikeSimmonds on Wed Jan 30 12:32:20 MST 2013
[FONT=Tahoma][SIZE=2]

---

Quote: th_shak
What is an industry standard? All AVR pins are tri-stated at reset so nothing of what I have described above is going to happen it is tested and working! Industry standard is to tri-state the pins and not make them high or low. You are right for the LEDs part, I should and I did connect them with the cathode to pin but for the step-up? What is your suggestion for that? I know that if I connect a pull down resistor to the particular pin I will not destroy my circuit but this is ridiculous, to have to connect pull down resistors.

---

A pull down resistor is pennies, how much does your 'destroyed' circuit cost!

My past does not included AVR, so I did not realise that their ports are handled differently to all the other MUC's that I have worked with.

I can only re-iterate: It is not going to help you to rant on about the way things are -- live with it and move on. If you don't want to do that, re-design with your AVR's and go to a different forum.




[/SIZE][/FONT]

[lpcware]

Content originally posted in LPCWare by serge on Wed Jan 30 00:51:29 MST 2013
First of all you are comparing citrons with oranges:eek:. An AVR mcu is not an ARM mcu. If they where equal they wouldn't have other names :rolleyes:.
So if you switch to another mcu then you should first read the manuals and all documentation concerning the core and the other building blocks relevant to this mcu. This way you would have noticed this different behaviour compared to an AVR.
So you really are to blame yourself for not having taken the time to learn this mcu.:mad:

[lpcware]

Content originally posted in LPCWare by th_shak on Tue Jan 29 11:49:27 MST 2013
What is an industry standard? All AVR pins are tri-stated at reset so nothing of what I have described above is going to happen it is tested and working! Industry standard is to tri-state the pins and not make them high or low. You are right for the LEDs part, I should and I did connect them with the cathode to pin but for the step-up? What is your suggestion for that? I know that if I connect a pull down resistor to the particular pin I will not destroy my circuit but this is ridiculous, to have to connect pull down resistors.

[lpcware]

Content originally posted in LPCWare by MikeSimmonds on Mon Jan 28 18:08:24 MST 2013
[FONT=Trebuchet MS][SIZE=2]Sorry to have to break it to to, but you are screwed.
This is a fact of life; no amount of "they should have" or
"they could have" is going to change the way a micro works.

All the micro controllers I have ever worked with adopt this strategy -- NXP, Atmel, ST,
Freescale (formerly Motorola), Hitachi, etc. do this. It is a defacto industry standard.

It may sound harsh, but you should always read, read, read, and read all documentation (user manuals, datasheets, app notes) over and over before you design hardware.
Going in blind has consequences as you found out the hard (expensive?) way.

I know that's easy to say, and occaisionally (even now) some gotcha trips me up.
I'm guessing from your post count, that you are new to this -- so treat this as a valuable
lesson learned. I doubt you will make [I]that[/I] mistake ever again.
If this is not the case, I can only say (respectfully) that you should have expected this.

For example: your LED's should be connected the other way round: Vcc to limit resistor to LED to port pin. Then a [I]low[/I] on the pin will light the led. Again, this is the normal (industry standard) configuration.

Mike

[/SIZE][/FONT]