resets tie up/down queries

Technical discussions related to any XMOS development kit or reference design. Eg XK-1A, sliceKIT, etc.
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resets tie up/down queries

Post by Folknology »

Some loose ends I need to clean up for Amino-Alpha

Looking at all of the Xmos designs using USB3318 I notice that ResetB is tied to ground via a 10K resistor. I also notice the signal driving it from the Xmos side is called PHY_RST_N suggesting an active low pin. Thus Its seems strange that the pin is tied permanently low? I am obviously missing something here as it is done in all of the Xmos schematics that use the 3318. Perhaps someone can enlighten me as to the operation of this feature.

I also notice that in some case TRST_n is also held low via a 10K resistor to hold the JTAG in reset, given that configuration would the JTAG be usable if one hooked up an xtag/xtag2 to debug it? If not usable I presume it is just being used as a built in xtag2 and thus not considered a useful feature, apart from burning the OTP.

Is there anything else I should be aware of regarding tie ups/downs of control and debug pins generally.


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Post by skoe »

As long as these reset lines are pulled low with a 10k resistor it's still possible to drive them high actively. But as long as the other side isn't there or is still tristated (e.g. while booting) these components are in a well-defined reset-state.

(disclaimer: I'm not a hardware-guy, please someone correct me if I'm wrong :) )