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C6747 RTCK Control

Chee Beng Ang
Intellectual 490 points
Other Parts Discussed in Thread: OMAP-L137

Hi,

I had a custom board that uses the RTCK (GP7[14]/RTCK) as the Watchdog input to my Processor Supervisory Circuit. To my surprise, I realised that latest document - SPRUFK4D - had removed RTCK from the pin. In the SPRUFK4C, the same pin is multiplexed with GP7[14] and RTCK. 

I would like to clarify this discrepancy.

Thanks.

Chee Beng

 

  • 0
    TI__Mastermind 24340 points

    RTCK is only necessary for the ARM, so it is still on the OMAP-L137 datasheet. Please see page196:

     

    “The device target debug interface uses the five standard IEEE 1149.1(JTAG) signals (TRST, TCK, TMS, TDI, and TDO), a return clock (RTCK) due to the clocking requirements of the ARM926EJ-S and EMU0 “

     

     

    For RTCK, the return clock function is required for OMAP-L137 emulation so it might not be a good idea to use the pin in GPIO mode. For C674x devices, at the beginning the idea is that the pin could act as a GPIO pin, however we learned that the pin behaves as RTCK out of reset, which is undesirable because you really don't want a GPIO pin toggling by itself if it is controlling something else on the board. That is why this pin was removed from the document you mentioned.