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K60 Without Clock connects through JTAG, with clock does not

Question asked by Charlie Heard on Mar 1, 2017
Latest reply on Mar 5, 2017 by Kerry Zhou

Hi,

 

We're working on an implementation using the K60 which has now prototyped and is going through testing. There's a slight oddity in getting it to run however.

 

The PCB as manufactured, (erroneously) misses the 0V connection of the 50MHz oscillator used to clock the MCU. This just ties the clock line to 3v3 and as such, the code falls over when it gets to the point that it's initialising the external clock.

When the clock is properly fed its 0V, it produces a nice clean sin wave which makes it to the pin on the MCU. However, with the clock enabled properly, the connection to the PC (through a JTAG adapter), fails to establish altogether.

We therefore end up in a strange situation whereby the JTAG interface only works when there is no extrenal clock... Adding the clock while already connected also kills an existing connection.

 

Has anyone encountered similar/do they have any ideas as to what might cause such behaviour?

 

Many thanks

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