ISP pin failures

[lpcware]

Content originally posted in LPCWare by frankee on Mon Jun 29 07:24:29 MST 2015
Hi,

I have the ISP pin on a custom board connected to a pushbutton via a test fixture pogo pin: there is no pull-up on the pin. I am finding that activating the ISP causes boards to fail: the pin shorts to ground internal to the LPC, and the LPC becomes bricked because afterwards it always boots to the bootloader. Is this a know problem, have others experienced this, is there a cure going forward?

Frank

[lpcware]

Content originally posted in LPCWare by MikeSimmonds on Mon Jun 29 09:37:36 MST 2015
You don't say what device or package you are using.

We have LPC1778FBD208 QFP.

The ISP pin has a 47K pullup to VC33 and a (normally open) jumper link to ground.

We have had no problems with this -- link on always boots to ISP ROM,
link off always boots to our flash boot loader [NB if flash is unprogrammed
of if the boot checksum is wrong, then it will still boot to ISP].

I conclude that you have an issue with the hardware.

It is a silly question, but you have verified that you have the correct ISP pin
for the device/package?

Cheers, Mike.

[lpcware]

Content originally posted in LPCWare by nerd herd on Mon Jun 29 08:29:10 MST 2015
Hi frankee,

The pin is shorted to ground internally inside the pin? Was this confirmed by measuring the voltage on the ISP pin with your 10K pull up connected?

[lpcware]

Content originally posted in LPCWare by frankee on Mon Jun 29 07:44:16 MST 2015
Hi,

Thanks for the response.

I have added a 10K pull-up to one of the failed boards, and it has no effect: the pin is connected(shorted) to ground internally and the program boots to the boot loader.

We have made 1000's of boards without the pull-up, and no problems, the problem is only when we short the ISP to ground in a fixture for testing/development, and afterwards most of the boards experience the problem described.

Frank

[lpcware]

Content originally posted in LPCWare by nerd herd on Mon Jun 29 07:29:38 MST 2015
Hi frankee,

The ISP is activated by detecting a digital LOW on the ISP pin. Since you do not have a pull up, when the button is not pressed, the pin will simply be floating (and still maintains the digital LOW when you pressed the button). Is it possible for you to connect the ISP pin to a pull up resistor to 3.3V?