topic Re: ISP behavior with P0.1 floating on boot? in LPC Microcontrollers

ISP behavior with P0.1 floating on boot?

lpcware — Wed, 15 Jun 2016 20:14:26 GMT

Content originally posted in LPCWare by Floyd42 on Sun Feb 02 07:39:53 MST 2014
What is the behavior with P0.1 floating on boot? The LPC810 user manual says that ISP mode is entered if it's LOW. But is does not say if an extern pull-up must be there or if the internal pull-up will be used. It seem is can be left floating and the user programm runs. That is also what they say at http://learn.adafruit.com/getting-started-with-the-lpc810/programming-the-lpc810-with-flash-magic.

For the default configuration the manual says about P0.1 (!ISP) and P0.5 (!Reset), that the internal pull-up resistor are enabled. Based on this, it appears to be save to leave them floating externally. Any official suggestion here?

Axel

Re: ISP behavior with P0.1 floating on boot?

lpcware — Wed, 15 Jun 2016 20:14:27 GMT

Content originally posted in LPCWare by lpcxpresso-support on Mon Feb 03 02:09:10 MST 2014
Don't leave ISP floating…

http://www.lpcware.com/content/faq/lpcxpresso/debug-design

Regards,
LPCXpresso Support

Re: ISP behavior with P0.1 floating on boot?

lpcware — Wed, 15 Jun 2016 20:14:27 GMT

Content originally posted in LPCWare by Floyd42 on Mon Feb 03 03:48:19 MST 2014
It just says: "Always ensure that you have a 10K to 100K Ohm pull up resistor on the ISP pin, otherwise you are unlikely to be able to make a successful debug connection." So what If one does not need a debug connection? And what in detail does this mean actually, what state is the device in if no successful debug connection can be made - ISP mode?

Axel

Re: ISP behavior with P0.1 floating on boot?

lpcware — Wed, 15 Jun 2016 20:14:28 GMT

Content originally posted in LPCWare by LabRat on Mon Feb 03 04:13:46 MST 2014

Quote: Floyd42
And what in detail does this mean actually, what state is the device in if no successful debug connection can be made - ISP mode?

You can find about 1000 threads here describing how beginners are confused because they've forgotten to pull-up ISP pin.

So sometimes somehow ending in ISP-mode is the result.

Sample: http://www.lpcware.com/zh-hans/content/forum/debug-problem-no-source-available

Re: ISP behavior with P0.1 floating on boot?

lpcware — Wed, 15 Jun 2016 20:14:29 GMT

Content originally posted in LPCWare by Floyd42 on Mon Feb 03 04:44:37 MST 2014
Refering to that thread, this guy says: "The electronics connected to PIO0_1 did pull it down, I fixed this and now it working again.". So this is not a surprise then and basically a user's fault. And adding an external pull-up then may also not help much when the unspecified "electronics connected to PIO0_1 did pull it down".

Please note that my question is about proper documentation and clarification what the bootloader does. So far it seem the bootloader does not modify anything, so the defaults hold and the pull-ups for Reset and ISP are on. And thus levaing the pin floating should be safe actually. Adding some more details in the UM for clarification may also help the beginners. But if things are not really explained, people start believing in magic and words some some forum gurus (that may not even apply to the chip they are using). Forums are also full of such examples......

Re: ISP behavior with P0.1 floating on boot?

lpcware — Wed, 15 Jun 2016 20:14:29 GMT

Content originally posted in LPCWare by LabRat on Mon Feb 03 05:17:34 MST 2014
Sorry, wasn't aware that this is an 'NXP UM documentation' thing. Just thought you are trying to get your stuff working and could profit from members which are drawing their own (working) boards since a lot of years...

Anyway, I'm not NXP so I'll abandon this thread.

Re: ISP behavior with P0.1 floating on boot?

lpcware — Wed, 15 Jun 2016 20:14:30 GMT

Content originally posted in LPCWare by Floyd42 on Mon Feb 03 05:40:43 MST 2014
Don't get me wrong, I appreciate any help (and surely also many others who find the posting).
Stuff is working fine for some time, now it's more about squeezing out as much as possible from the chip and reducing any unneeded external components. So it comes to the question how much can be removed savely from the ISP/Reset pins and how they can be used savely without leaving the specs of the bootloader. Trying to minimize the surprises when a new revision comes out, and identify things that are clearly marked as not-guaranteed, e.g. like http://www.lpcware.com/content/forum/lpc810-question-about-connect-acmpo-sct-input#comment-1131496

Axel

Re: ISP behavior with P0.1 floating on boot?

lpcware — Wed, 15 Jun 2016 20:14:30 GMT

Content originally posted in LPCWare by LabRat on Mon Feb 03 05:59:01 MST 2014

Quote: Floyd42
Trying to minimize the surprises...

...then the answer is simple: add 2 simple 402 to pull-up ISP and Reset.

Re: ISP behavior with P0.1 floating on boot?

lpcware — Wed, 15 Jun 2016 20:14:31 GMT

Content originally posted in LPCWare by Floyd42 on Mon Feb 03 06:33:40 MST 2014
Hi,

right, in the end this might really be the best.

Axel