topic SWD / JTAG adapter without resistors in Kinetis Microcontrollers

SWD / JTAG adapter without resistors

alexeypanteleyc — Wed, 31 Aug 2016 06:06:45 GMT

Hello!

Could you please advise if the following schematic is recommended for SWD / JTAG adapted for Kinetis MCUs (MKM33):

HardwareDebugConnections - ** Code Red Support Site **

Or it's better to use another one?

Is it critical to use pull-up and pull-down resistors for SWCLK and SWDIO lines? May the adapter work without them?

Thanks,

Alexey

Re: SWD / JTAG adapter without resistors

alexeyusoltsev — Wed, 31 Aug 2016 06:20:45 GMT

Hi Alexey!

As for SWD you no need to add any resistors. At least it worked for me for kv10,mk10,mk22,kv30,kv31,kl27 MCUs. And dont mess with reset-you need reset_b pin to trace to reset of JTAG.

Best regards and "yda4i",

Alexey.

Re: SWD / JTAG adapter without resistors

Robin_Shen — Thu, 01 Sep 2016 02:57:13 GMT

Hi Alexey,

SWD_CLK is pulled down internally, and SWD_IO is pulled up internally. (You can get this information from MKMXXZXXACXX5RM.)

It isn't critical to use pull-up and pull-down resistors for SWCLK and SWDIO lines. The adapter may work without them.

The external pull-up shown in some diagrams is for potentially noisy environments, and should be on the order of 10kΩ.

From the Kinetis L Quick Reference User Guide (KLQRUG):

The RESET_b pin should have a 100 nF capacitor close to the MCU for transient protection. It has a weak internal
pullup, but an external 4.7 kΩ to 10 kΩ pullup is recommended.(From the Kinetis L Quick Reference User Guide KLQRUG)

Best Regards,

Robin

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