topic Re: SWCLK - External pull-down? LPC1549, SWD in LPC Microcontrollers

SWCLK - External pull-down? LPC1549, SWD

lpcware — Wed, 15 Jun 2016 17:11:06 GMT

Content originally posted in LPCWare by Terje on Mon Nov 30 14:32:21 MST 2015
In the recommended design (fig 49. in the datasheet) it is shown an external pull-down on the SWCLK pin. However, in the user manual, table 628 it says that SWCLK is internally pulled up. On the page "Design Considerations for Debug" (https://www.lpcware.com/content/faq/lpcxpresso/debug-design) it says the following:Note for TCK/SWCLK, although a pull-down is recommended, you can alternatively use a pull-up. The main thing is that it does not float. Note in particular that if the MCU provides an internal pull-up on this signal, then adding an external pull-down on the board is not recommended. What is correct? Should it be pulled up or down?

Re: SWCLK - External pull-down? LPC1549, SWD

lpcware — Wed, 15 Jun 2016 17:11:06 GMT

Content originally posted in LPCWare by cgroen on Wed Jan 13 06:15:57 MST 2016
Terje,
did you get any feedback on this ?
On my own LPC1549 designed boards I have no pullup or down on either SWDIO or SWCLK and it seems to work perfect

Re: SWCLK - External pull-down? LPC1549, SWD

lpcware — Wed, 15 Jun 2016 17:11:07 GMT

Content originally posted in LPCWare by Terje on Wed Jan 13 08:04:38 MST 2016
Hi,
No, I did not get any feedback so thanks for your reply. I decided drop the pulldown for SWCLK and it seems to work fine here also. I do still have a pull up on SWDIO. I do believe the recommended design in the datasheet is wrong so I had hoped someone from NXP could have commented on this.

Re: SWCLK - External pull-down? LPC1549, SWD

lpcware — Wed, 15 Jun 2016 17:11:08 GMT

Content originally posted in LPCWare by R2D2 on Wed Jan 13 09:36:14 MST 2016

Quote: Terje
I do believe the recommended design in the datasheet is wrong...

We don't use SWD pullups since LPC15xx was released (February 2014) :O