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When is EZPort mode selected during reset on K20?

Question asked by GRAHAM JORDAN on Feb 9, 2016
Latest reply on Feb 12, 2016 by Jorge_Gonzalez

I using K20 (MK20FX512VLQ12 specifically). It is in a system with other processors, with a 'Master' processor that can put the K20 in EZPort mode to reprogram it.

 

What I can't see from the documentation is exactly when the \EZP_CS line is checked to determine if is going into EZPort mode.

 

If the external reset pin is driven low, and then goes high. When is the \EZP_CS checked?

 

I see from the reference manual (K20P144M120SF3RM Rev. 3, November 2014):

"The device's functional mode is controlled by the state of the EzPort chip select

(EZP_CS) pin during reset."

In the boot sequence (step 4) it says:

"EzPort mode is selected instead of the normal CPU execution if EZP_CS is low when the internal reset is deasserted."

But this sequence seems to refer to power-up explicitly. As it also indicates it looks at the \RESET pin after this (in step 5).

 

When is 'internal reset' deasserted, relative to power-up, and relative to having \RESET pin driven low and then high externally?

 

Thanks.

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