14 Oct 2010



I'm using an mbed with a 40x2 lcd display and it works fine, when it works. But I think i'm inadvertently triggering the bootloader when i reset the mbed, I get gibberish on my serial terminal, and if i type '?' It comes back with Syncronised, which is the bootloader saying that it's sync'd baudrates.


So, Which pin on the mbed is the one the triggers the bootloader? the LPC17xx docs says it's P2.10, but i don't know what that maps to.


also should i use a pullup or pull down resistor (i guess it depends on what i'm using the pin for)?

14 Oct 2010

P2.10 isn't routed out onto one of the 40pins. It's internally connected to the backend I/F chip. The Mbed circuit diagram is here:-

15 Oct 2010



So anyone got any idea why my mbed is going into bootloader mode and not running?

It looks like it only does it with certain of my programs, so i guess the programs crash?

I have a statement to switch an led on as the 1st statement and it dosn't come on, so some kind of very early runtime error?

15 Oct 2010 . Edited: 15 Oct 2010

Hi Jasper,


As per Andys, email, the ISP pin (P2.10) is active low and sampled on reset. It is hooked up to a pin on the interface that should be tristated. The external 10k resistor (R1) should therefore prevent bootloader mode.


Below is a screen grab of the bottom of the board. The red traces/pads are for R1, the pullup resistor. I think my first port of call would be to check that this resistor is in place, and that it is connected correctly. You might want to try getting out your multimeter, and ensuring that the top of the resistor is connected to +3.3v (probe to the middle pin of the regulator on the left when looking at the top of the mbed, NOT Vout, that is supplied by a different circuit). Then check that the bottom of that resistor is connected to the P2.10 of the LPC1768 (third pin from the right on the edge of the LPC1768 nearest the USB connector).


Let me know what you find.








18 Oct 2010

The resistor is there and connected.


I think the problem is more software related - what would happen if a class in the downloaded code did something like a divide by zero in the initialiser? Would that trigger a drop into the bootloader?


Some of the code that i write works, and some does the syncronised thing.


Hmm, maybe i need to mount the device with the sync option, repeatedly downloading the same code makes it work after a few tries. (This is with chrome on ubuntu lucid/10.04).