Disabling BDM interface on MCF5235

[set_au]

I use the BDM interface for debugging but when I am not debugging I would like to turn off the PST[0..3] and PSTCLK lines as these switch continually at up to the core frequency causing horrible emissions. I expect there is a way to disable these lines from the firmware but I haven't been able to find any information anywhere. Is there a way to do this?

Thanks
Scott

[SimonMarsden_de]

The Chip Configuration Register (part of the CCM module) has a bit called PSTEN which lets you turn off PST/DDATA.

There's also a DISCLK bit in the Synthesizer Control Register (part of the Clock module) which lets you turn off CLKOUT.


Hope this helps


Simon

[set_au]

I have tried disabling the PST lined with the PSTEN bit but without any luck. I set CCR to zero first thing after the reset entry point -

start:
  move.l #MCF_CCM_CCR,a0
  move.w #0x0000,(a0)

I have tried this both with the BDM interface connected and disconnected and still get very high frequency signals on the PST lines. Are there any other tricks to get these lines disabled?

Thanks again
Scott

[TomE]

The eventual solution to this SIX year old problem was to pull JTAG_EN high with a resistor, and have the JTAG pod pull it down when plugged on.

It looks like the PSTEN bit in the MCF5235 CCR simply doesn't work, AND the Manual (latest Rev 2, 7/7/2006) has never been corrected to say this AND there's never been a new version of the Reference Manual Addendum (latest Rev 2.2, 5/23/2007) to correct this either.

This post from 2009:

Disable PST/DDATA signals on MCF5274

says "You can't disable the PST signals on this part using that register" and "Will update errata manual.".

Four years and waiting for that update.

I'm guessing that because a Freescaler said "it doesn't work in the MCF5274" then maybe it is also broken in a different but related part.

Tom

[set_au]

Simon,

I tried disabling CLKOUT with DISCLK but that seems to turn off the RAM clock as well. I'll try the PSTEN bit. Thanks for your help.

Scott

[Arev]

Hello,

CLKOUT is used as SDRAM Clock and can't be disabled.

To disable BDM Interface, I use a jumper on JTAG_EN signal.

when JTAG_EN = 0, BDM interface is Enable and all BDM signals are Enable.

when JTAG_EN = 1, BDM interface is Disable and CLKOUT and all Clocks signals are Disable on BDM.

So when i'm not Debugging, i just disable the BDM Interface.

I Hope this helps..

Bye