topic Re: Kinetis K61 DDR_CKE pull-down in Kinetis Microcontrollers

Kinetis K61 DDR_CKE pull-down

panin — Tue, 12 May 2020 17:44:46 GMT

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

Re: Kinetis K61 DDR_CKE pull-down

jingpan — Fri, 15 May 2020 06:27:08 GMT

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

Re: Kinetis K61 DDR_CKE pull-down

panin — Sat, 16 May 2020 07:59:13 GMT

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

Best regards,

Yuri Panin