LPC824 Power question

[lpcware]

Content originally posted in LPCWare by lavanyasubbu on Wed Jun 17 08:10:43 MST 2015
Team I am using LPC824 to connect to an external GPS GPRS module. We are seeing a strange occurrence. Need you help please.

Our logic is as follows on LPC824

1) Wait for 5 seconds (Give the whole system time to settle on power up)
2) Pull the power key of the GPS GPRS module using a GPIO pin (p0_27)
3) Wait for 5 seconds.
4) Go through process of setup initialize and loop


Problem: When in step #1 I power cycle for a short enough duration (say about 500mS) LPC824 just hangs. It neither restarts nor does it continue with the processing. On our hardware (since its automotive) our capacitance is about 470uF to stop fluctuations. I am not sure if thats causing a problem


Please note that i have a 4.7kOhm resistor between the GPIO line and the GPS/GPRS's pwrKey

Appreciate your help

Best Regards
Surendar S

[lpcware]

Content originally posted in LPCWare by lavanyasubbu on Tue Jun 23 01:48:03 MST 2015
Joe
I am using Mbed. I have very little debug capcability.  As I told you I am a complete newbie and didnt bring any pins out. I can try bringing the swd pins.

I will try the turning GPIO on and off too

THanks for your time.

Best Regards
Surendar

[lpcware]

Content originally posted in LPCWare by jdesbonnet on Mon Jun 22 02:15:29 MST 2015
Do you have a debug probe (eg LPCLink) that you could hook up to the Serial Wire Debug pins? You could try to see where the program counter is when it's hanging. If that isn't working it would indicate some sort of hardware problem alright.

Do you have an oscilloscope? (personally I think it's almost impossible to do embedded development without one). I often find using a debug pin handy. I'd pulse it to indicate that a certain point is reached. For example I can pulse it once when entering an interrupt service routine, and twice on each iteration of the main loop... etc. You could try to pulse a pin at some of the critical points of your boot procedure. Of course you need to initialize the GPIO first before that will work.

[lpcware]

Content originally posted in LPCWare by lavanyasubbu on Sun Jun 21 19:54:20 MST 2015
R2D2 and Joe
I tied the ISP pin and the reset pin and am still having the same problem

[lpcware]

Content originally posted in LPCWare by lavanyasubbu on Sat Jun 20 01:48:16 MST 2015
R2D2,
Thanks. Will change our circuits to include the pull up on ISP Pin. We dont use the other ones. I thikn i can leave them the way it is (if present in our chip)

Any other reasons why this is happening on 824. I have tried on 812 and it doesnt seem to happen? May be a "true" problem with LPC824 and this has not been "caught'?

Best Regards
Surendar
PS: Saying I am a novice in hardware design is itself bragging. I know next to nothing but I appreciate that people taking time to answer my questions

[lpcware]

Content originally posted in LPCWare by R2D2 on Fri Jun 19 07:40:33 MST 2015

---

Quote: lavanyasubbu
I am guessing its not in ISP mode.

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:D

Read:

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

and add 10k like the rest of the world...

[lpcware]

Content originally posted in LPCWare by lavanyasubbu on Fri Jun 19 07:25:07 MST 2015
Hello Joe Again
I replicated the problem and tried to to see if I could use FlashMagic to read the device's signature (to see if it moved to ISP mode). But it could read the Device ID. I am guessing its not in ISP mode.

Reason i did that  (without adding the pull up resistor) was to confirm that it actually was moving to bootloader mode

Any other diagnostics I need to run?

BTW if I need to add a resistor, will a 10kOhm resistor be good? I am reading about pull-up resistor and it says it must be 1-10th of the the pin impedance. The LPC 824 doc at one place says the imp is about .1M Ohm. Am I right in this


Best Regards
Surendar

[lpcware]

Content originally posted in LPCWare by lavanyasubbu on Fri Jun 19 04:28:28 MST 2015
Hello Joe
Thanks for responding. Please pardon me for this super dumb question.

When you say "tie it high" do you mean connect by hardware to a high line with a resistor" or pull it high in the program?

Best regards
Surendar

[lpcware]

Content originally posted in LPCWare by jdesbonnet on Wed Jun 17 09:55:14 MST 2015
My guess is that it is entering the serial bootloader mode. Make sure the serial bootloader entry pin (aka PIO0_12 on the LPC824) is not floating. Tie it high to prevent unintended entry to the bootloader during power up / reset. Also tie RESET (aka PIO0_5) high if not in use.