LPC824 SWDIO pin causing issue when set to GPIO Output High

[sibinthomas]

Hello Everyone,

I am using lpc824 (lpc824M201JDH20J) controller on my custom board and I am trying to set the PO_2 (SWDIO) as GPIO output and P0_3 (SWCLK) as GPIO input pins. My board is powered with 2.8V supply with 47K pullup on the RESET. I have disabled the default function of SWDIO and SWCLK using the switch matrix. I have three leds connected to output pins (P0_1, P0_8 and P0_9). On startup, just after configuring these pins and making P0_2 High, in my while loop i am reading the status of the input pin (P0_3) and toggling the leds.

The problem is when I make PO_2 high and if i reset the controller 2 or 3 times my other pins are not getting configured properly. Like LEDs (P0_8 and P0_9) not going high and low and my input P0_3 is always reading low. but LED P0_1 is working. This issue happens only when i configure P0_2 as output and high and do reset few times. The code is working as expected if my P0_2 is output and low. I am attaching my code where if PO_2 is made high this problem occurs and if P0_2 is low everything works. Is there any problem with the P0_2 (SWDIO) making output and high? Why on several reset the pins are not getting configured properly? Any suggestion would be helpful.

Thanks.

[jeremyzhou]

Hi Sibin Thomas,

Thank you for your interest in NXP Semiconductor products and for the opportunity to serve you.
Workaround:
After disabling the default SWD functions of the P0_2 and P0_3, you should remember pull-down the P0_4 to the low state prior to resetting the MCU, after that, release the P0_4.
Please give a try.
Have a great day,
TIC

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[sibinthomas]

Thanks for your reply.
I was unable to sort out the issue even after doing the changes you insisted. I would also like to inform that there are no external Pull up/Pull down resistors on any of the RST,ISP,SWDIO,SWCLK pins.
Is using the SWDIO & SWCLK as an GPIO function causing this problem?

[jeremyzhou]

Hi Sibin Thomas

1) Is using the SWDIO & SWCLK as a GPIO function causing this problem?
-- Yes, there's a bug in the chip and the corresponding workaround is shared before.
Note: In the workaround, reset the MCU via the reset pin.
My colleague and I have both validated the workaround with LPCXpresso LPC824 board.
Have a great day,
TIC

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[sibinthomas]

Hi jeremyzhou,

Thank you for your support.

I am trying the workaround you suggested, just after the disabling SWD functions I am enabling the internal pull-down using the IOCON function.

Then I am configuring SWD pins as GPIOs (P0_3 input and P0_2 output high). After this in my while loop I am toggling my three leds (P0_8, P0_9, P0_1). Still my problem happens after few resets. Am I missing something or should I connect an external pull-down on P0_4 ?

Is this bug and workaround has been documented anywhere. If it is available can you please provide the link, because I couldn't find this issue in Errata sheet of lpc82x.

Thanks.

[jeremyzhou]

Hi Sibin Thomas,

The errata hasn't included the bug now, however, this bug had already been confirmed by IP design team.
To avoid triggering this 'bug', the P0_4 need to be pulled down on reset, just as same as pull down the ISP pin to force the MCU to enter the ISP mode.
I was wondering if you can record a video of the testing process, maybe I can find what step you miss.
Have a great day,
TIC

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[sibinthomas]

Hi jeremyzhou,

Thanks for the Quick Reply.

Do you mean to pull down the P0_4 externally, Or only the internal Pull down can Solve this issue?

Thanks,
Sibin Thomas

[jeremyzhou]

Hi Sibin Thomas,

Thanks for your reply.
1) Do you mean to pull down the P0_4 externally?
-- Yes, it needs to pull down the P0_4 externally.
Have a great day,
TIC

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