JTAG programming without external clock

[palmering]

Hi,

I'm trying to program a K64F with Cyclone Max via JTAG.

The K64F has a KSZ8081RNA Ethernet controller as an external clock source similar to Freedom board FRDM-K64F.

If the ethernet controller is disable (i.e. it does not generate clock) the K64F couldn't be programmed.

However, if the ethernet controller is enable (i.e. it generates clock) the K64F is programmed right.

So the question is: 

Is it necessary to provide an external clock source to program the K64F via JTAG?

Thanks in advance!

[xiangjun_rong]

Hi,

As you know that the K64F has internal 32KHz and 4MHz internal reference clock, in default state after Reset, the MCG works in FEI mode, in other words, it uses internal FLL output(based on 32KHz internal reference clock) as the core/system clock. If you use external clock from EXTAL pin, you have to use firmware to change the MCG setting.

In conclusion, it is not necessary to provide an external clock source to program the K64F via JTAG.

Pls check the power supply and ground pins connection for your issue.

Hope it can help you

BR

Xiangjun Rong

[palmering · Accepted solution]

Hi Xiangjun,

Yes, you helped me! What you said is totally true.

I realized that I had connected the pin 38 (PTA4/EZP_CS_b) to GND with a pull down resistor. A low state in this pin enables the EZPort flash programming mode, so I couldn't program the flash via JTAG.

I wanted to use this pin as a GPIO so I forced a low state with a pull down resistor before reset, I didn't realize that this pin had a function (wrong decision!).

Finally I took off the pull down resistor and everything works. This is because this pin has an internal pull up by default and I could leave this pin open.

Thank you very much.