Kinetis K61 DDR_CKE pull-down

[panin]

Hello everyone!

Consider the following scenario:

• ...
• Application code is executed from the lower half of the DDR2 memory.
• At some point in-application programming is executed and a new application is loaded into the upper half of the DDR2 memory.
• DDR2 memory is put into the self refresh mode and MCU is reset (reset is needed to initialize the core and the used peripherals to a known state).
• DDR2 controller is initialized and control is passed to the application in the upper half of the DDR2 memory.
• ...

Is the external pull-down resistor on the DDR_CKE necessary to keep the DDR2 memory in self-refresh mode in this case after MCU is reset? What might happen if there is no pull-down?

In case it matters MCU is MK61FX512VMJ12 and DDR2 memory is MT47H128M16RT-25E-IT.

Best regards,

Yuri Panin

[jingpan · Accepted solution]

Hi Yuri,

Yes, I think an external 10k pull-down resistor is needed. The DDR_CKE pin of K61's default state is DISABLED. That is a high-impedance state. The TWR-K70 board also has this pull-down resistor.

Regards,

Jing

[panin]

Just as I suspected. Thank you very much, Jing!

Best regards,

Yuri Panin