A customer using the TPS65920 asked the following two questions.
"The data sheet says that the TEST pin is used to switch from GPIO state to JTAG stat on certain pins. One of those pins happens to be the card detect pin for the SDIO interface. I wanted to support JTAG and the SDIO interface. The data sheet says pick the state with a pull up or pull down on the test pin but does NOT say which one is which?
Also, could we somehow alter the test pin when the JTAG connector is plugged up in order to change the state to JTAG, and then back to GPIO (or MMC2 card detect) when the JTAG connector is not connected? There by using both functions"
Thanks,
Faizul Bacchus
JTAG is generally used in factory for checking the scan chain. Is this the purpose you need to use JTAG. This JTAG should not be confused with any type of emulator JTAG or such. Let me know what you want to do and why are you looking at using both modes.
In test mode the device power-up etc is completely different, you cannot toggle between test and application mode. Test mode is used only during device validation/verification. I do not recommend any customer to use test mode.
Regards,
Gandhar.
Gandhar,
Faizul asked this question for me, and I will supply the response.
In circuit testing during the manufacturing process is what I was after. I didn't know if I should chain the companion chip JTAG with the OMAP JTAG, or leave it by itself, and let the test fixture access it independently. If it is chained with the OMAP JTAG, then when the OMAP goes to JTAG mode, something would have to make sure that the companion chip also enterd JTAG mode (via the TEST pin). Again, I guess that could be accomplished by the test fixture doing both operations simultaneously.
I think I will just supply test points for the companion chip JTAG without chaining. This should also simplify debugging by not having to tell the emulator that there is something else in the chain.
Jerry
It is ok to use JTAG without chaining. If it is simple then it is good to implement that way.
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