Trace versus SDHC on K64

[marks]

Looking at the K64 tower board schematic, it has the SDHC card data and clock tied to the JTAG trace data and clock lines.  When we spin our own board for this project, we do want to keep the SDHC socket but also want to be able to use the trace capability and will only have the JTAG/trace connector, not the tower board’s separate K20 MCU for the USB debug interface.  (The SDHC and trace functions are shared on the same dedicated pins on the MCU, so this is obviously something that Freescale has thought about.)

I’m wondering how well these will coexist with each other and what we will have to do so we can debug and use an SD card without losing the trace capability?

If you have any guidance or can point to application notes or other information, I’d really appreciate the hints.

Thanks!

Mark

[Kan_Li]

Hi Mark Sample,

If you refer to the K64 data sheet, you may find alternative pins for trace function on PTA[6..10]. Please refer to the following for details.

Hope that helps

Have a great day,
Kan

Freescale Technical Support
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[mjbcswitzerland]

Mark

The trace pins are MUX functions that the SW much set up (the pins don't default to trace function) and the trace pins are usually available on multiple pins.

For example SDHC0_D0 and TRACE_D3 are both on the port PTE1. This defaults to ADC input and so the software decides whether to use it as SDHC or Trace.

In your case you will probably prefer to use the pin as SDHC_D0 always and so you can instead select TRACE_D3 to be on PTA7 instead, which is an alternate location (and hopefully you won't be using that for one of its other functions).

It will however also be housing dependent as to whether there is a trace connection and how many alternatives the trace pins have - some smaller housings may be less flexible since they simply don't have all pins available.

Therefore if you are now defining the circuitry you may be able to work out the pin utilisation so that you can keep the trace lines aways from the SDHC interface and then have no restrictions.

If this is not possible the software will need to "temporarily" disable SDHC mode in favoir of the trace functionality. Once debugging has completed it can then re-enable the interface.

Regards

Mark

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