LPC1763 failing to enter ISP sometimes(?)

[lpcware]

Content originally posted in LPCWare by Lowe on Wed Nov 04 14:32:42 MST 2015
Hi,

We have a design using a LPC1763 connected to a SOM (System On Module). The SOM has the possibility to control the ISP interface on the LPC (RESET, P2.10 and UART).

The problem we experience is that some times the LPC does not enter ISP mode. We have many designs using the ISP (in production) without any problem. Also we have measured all the signals many times and they are perfect.

My guess is that the LPC fails to enter the ISP mode (for some unknown reason) and then tries to start the firmware but fails in some way.

We have also verified that all power and other signal are good. No protection fuses are set. We have tried high, medium and low baudrate.

The only time the ISP works is directly after power up, but when toggling the RESET with P2.10 low, no ISP communication can be established.

Best regards,
​Lowe

[lpcware]

Content originally posted in LPCWare by Lowe on Mon Nov 09 06:01:17 MST 2015
Well, we *might* have found the issue.

It looks like the WD flag might be raised even during "normal" conditions. A raised WD flag will force the boot sequence to bypass the ISP.

/Lowe

[lpcware]

Content originally posted in LPCWare by MikeSimmonds on Thu Nov 05 07:47:17 MST 2015
Just a thought, is your remote controlled reset long enough.
ISTR that a manual (not neccesarily 176x) says that it takes up to 3? ms
for the ISP to be recognised.

Mike.