KE04 SWD Interface Question

[jimmorris]

I just finished a design using a Kinetis KE04 series part (MKE04Z8VTG4), and came across this footnote in section 9.2 (Debug port pin descriptions) of the KE04 reference manual for this part:

1. The pad library of this device does not support on-chip pull down; the SWD_CLK pin supports only pulp controlled by PTAPE0, external pulldown resistor is required to fully support the SWD protocol.

Yet I have looked at the schematics for the FRDM-KE04Z board with the 24 pin version of this chip on it, and do not see any pulldown in the circuit on the SWD_CLK line of the device.

Can anyone comment on this, as I have a completed set of gerber files for my PCB, but don't want to pull the trigger on an order until I know whether I need to add a pulldown resistor on this signal. Right now I just have RESET (PTA5), SWD_DIO (PTA4), and SWD_CLK (PTA0) going to the respective pins on a Mini-10 ARM header, along with GND and VCC.

Thanks!

Jim

[kerryzhou]

Hello JIM Morris,

Normally, in the new KE04 design, customer should:
1. SWD_DIO add 4.7K to 10K external pullup resistor, internal pull up is weak, it is better to add external pull up.
2. SWD_CLK add external pulldown resistor resistor, because the pin don't have the internal pull down.
3. Reset_b pin, 4.7K to 10K external pullup resistor, and 0.1uf capacitor to ground.
4, NMI pin, external 4.7k to 10K pull up.
You said FRDM-KE04 don't have the exteral pull down in the SWD_CLK pin, you will find, actually, the SWD_CLK also add to the 74LVC125ADB chip which is connect to the on board opensdsa.
Anyway, to work stably, I suggest you do like the above 4 items which I mentioned.

Wish it helps you!

If you still have question about it, please let me know!

Have a great day,
Kerry

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[jimmorris]

Thanks for the tips.  I guess I didn't look closely enough at the FRDM-KE04 schematic to catch some of that.  My other Kinetis designs have been with the K10 series, and I didn't have to use any external resistors with that device, or at least I got away without using any.

[kerryzhou]

Hello JIM MORRIS,

   k10 have some difference with the KE series, especially the SWD_CLK pin. K series have the internal pull down, but the KE series don't have it.

  For other external resistors, in the application, to work stably, it is better to add the according external resistors.

Wish it helps you!

If you still have question, please let me know!

Have a great day,
Kerry

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Note: If this post answers your question, please click the Correct Answer button. Thank you!
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