Is it necessary to drive DE_B to enter debug mode?

[adevries]

Hello,

I'm working on configuring the 8M Mini to support boundary scanning and debug mode. Section 4.11.7 of the reference manual talks about constraints related to the JTAG interface, and it says, "DE_B is an IO pin with pullup and care must be taken of the direction when driving this signal."

I did some more investigation and found out that signal SJC_DE_B (which is Secure JTAG Controller Debug Enable#) can be multiplexed to pad GPIO1_IO02, which I am currently using as my watchdog signal WDOG_B.

In the 8M Mini hardware design guide, it talks about needing to control signals BOOT_MODE0, BOOT_MODE1, JTAG_MOD, and TEST_MODE for boundary scanning. However the guide makes no mention of a DE_B pad or an SJC_DE_B signal needed to support any additional features like boundary scanning or debug mode, so I'm a little confused by this discovery.

Do I need to multiplex SJC_DE_B to pad GPIO1_IO02 in order to put the 8M Mini in debug mode? If so, do I need to drive this signal high or low? Is it possible to have this pad work as both WDOG_B and SJC_DE_B?

I would appreciate any guidance anyone has on how to enter debug mode for the processor, if I need signal SJC_DE_B to enter debug mode, and how to drive this signal if it's needed.

Thanks

[igorpadykov · Accepted solution]

Hi adevries

>Do I need to multiplex SJC_DE_B to pad GPIO1_IO02 in order to put the 8M Mini in debug mode?

no. It can be left unconnected. SJC DE_B pin is rarely used signal and described in
sect.56.2.3 Accessing ExtraDebug Registers i.MX6DQ Reference Manual
and arm documentation as Debug Request/Debug Acknowledge pin
ARM Information Center 

i.MX 6Dual/6Quad Applications Processor Reference Manual

> Is it possible to have this pad work as both WDOG_B and SJC_DE_B?

no

Best regards
igor
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