understanding USBDM target vdd control option

[gschelotto]

Hi,

I usually program/debug E02Z, KL03Z, KL05Z and others Kinetis MCUs with USBDM and FRDM-KL25Z. However I don't understand the Target Vdd Control option (Off, 3.3V, 5V) in the KDS 3.2 debug configuration. If I select the Off option I expect to have to power the target processor externally (am I wrong?) but It's not needed. Despite chosing Target Vdd Control=Off the target processor is powered by the FRDM-KL25Z with no problem.

How can I disable the Vdd in FRDM-KL25Z in order to power the target processor externally?

regards,

gaston

[pgo · Accepted solution]

Hi Gaston,

Some USDBM hardware versions have target Vdd control and some don't.  The FRDM_KL25 does not have the hardware required to switch the target Vdd.  The setting is ignored.  If you wish to use the FRDM_KL25 with an externally powered target you should check the schematic for the board and cut the appropriate link and add a jumper.  If the taregt is not operating at 3.3V you should carefully check the schematic to see if the interface works for other voltages.

See:

http://www.nxp.com/assets/downloads/data/en/schematics/FRDM-KL25Z_SCH_REV_E.pdf 

(I believe J3 provides target)

The code for the USDBM plugin for KDS is written in a general fashion and the launch configuration has that option to support other hardware versions. For example the K22F does have basic target Vdd control and will respond to the settings.

It did not seem sensible to query the interface to determine it's capabilities as the interface (e.g. FRDM board) may be changed without opening the launch configuration.

In the stand-along programmer the options are disabled if the interface does not support that feature.

bye

[gschelotto]

Great! Thank you for the given support. Besides K22F are there another family with this feature?

BTW in order to disable the power provided by FRDM-KL25Z (3.3V) you have to remove J4, R81 and R73. Doing this you need to power the target processor externally. It's very usefull when debugging 5V processors to avoid undesired current drifts caused by different (3.3V / 5V) power sources.

regards,

gaston