Regarding K61 Clocks

[sithara]

I am using MK61FN1M0VMJ12 for
my design. I need to run the processor @ 120MHz. Also using DDR2 memory and RMII
ethernet interface of the processor. Please advice on the proper clocking of the
processor.

I have seen three external oscillator connections:
1.
XTAL0/EXTAL0
2. XTAL1/EXTAL1
3. XTAL32/EXTAL32.

I have connected
a 32.768kHz crystal on the XTAL32/EXTAL32 pins for RTC operation.
What about
the two XTAL pins?
Shall i need to connect both?
What is the exact
crystal/clock value if i need DDR2 & RMII LAN in my application?

[sithara · Accepted solution]

Hi..

Please see below the response from Freescale Technical Serice Request i got,

As the RMII clock source is fixed to OSC0ERCLK and must be 50 MHz, so If RMII is applied in your application, XTAL0/EXTAL0 must be used and a 50MHz oscillator is the best choice. For DDR, there are two clocks for this module, one is HCLKs which can be from multiple clock sources (selected by registers in the MCG module, for example, MCG_C11[PLLCS]), but CLK/CLK2x is
always from the PLL1, so XTAL1/EXTAL1 is also needed for your case, you may use a 15MHz crystal to get the max 150MHz DDR clock.

Regards,

Sithara