Reference Clock

The C6678 EVM uses two CDCE62005s to generate all the clocks needed by the C6678.  This includes the three system clocks, CORECLK, PASSCLK, and DDRCLK, as well as the three serdes reference clocks, MCMCLK, PCIECLK, and SRIOSGMIICLK.  Note that the CORECLK and DDRCLK are required for all C6678 designs but the rest of the clocks are needed based on which peripherals that you are using.  See the hardware design guide for more information on the clocks and their stability requirements.

Hello ,

In the EVM C6678  , How can I provide reference clock from external source through AMC connector to the DSP , instead of being provided by the default clock coming from

the local oscillator CDCE62005 of the DSP.

thank you

In the latest version of the EVM there was a feature added to support the use of a clock source from the AMC connector.  If you have the A104-1 revision of the schematic you will see that the TCLKB+/- p pair on the pins 77 and 78 of the AMC connector are routed to the PRIREF+/- clock inputs of the CDCE62005.  The CDCE62005 can be programmed to accept this input as the reference clock which is then used to generate all of the clocks needed by the C6678.  This capability is not present in earlier versions of the EVM.

If the frequency present on the PRIREF+/- pins is not 25MHz then the CDCE62005 will have to be reprogrammed to generate the needed frequencies for the C6678.  If a clock is present at the PRIREF+/- input to the CDCE62005 the part is presently programmed to automatically prioritize that input over the 25MHz crystal connected to AUXIN.  Note that this is a new feature and validation is still on-going.  The automatic use of the PRIREF+/- clock input may require an upgrade to the CDCE62005 to operate in this manner. 

Bill,

Yes we have the pin  coming from the AMC , but we found that both the AMC pin and the CDCE62005 pin enter to a multiplexer to select what clock to enter to the DSP ,

how can we select either the AMC pin or CDCE62005 pin to be used ?

thak you Bill,

I mean just if there is a switch to enable either AMC pin or CDCE62005 pin . in the EVM C6678 ??

As I stated in my previous message, if a clock from the AMC is present on the PRIREF+/- pins of the CDCE62005 Advantech has programmed it to prioritize that clock input over the AUXIN.  If you need to change the programming of the CDCE62005, the instructions for accessing the registers are in the Technical Reference Manual.  The webpage for the CDCE62005 has a tool you can use to determine the register values for setting up the PLL and the internal muxes.  Register 5 has three bits used for the SMART MUX control.  Currently I believe that Advantech has these three bits set to 111 for Auto select with the clock prioritization set to PRI first, then SEC and then AUX.  The CDCE62005 should sense your clock from the AMC connector and use that clock when it is present.