4.4.2. Setting the Clock Source for SCbus Systems

Perform the procedure described below to change the default clock settings for an SCbus mode system:

1. To access the clocking settings in DCM, double click Bus-0 under the TDM Bus in the DCM tree structure of configured devices. This displays the TDM Bus Configuration property sheet for Bus-0 (Figure 12).
2. Ensure that the TDM Bus Type (Resolved) parameter is set to SCbus. If the current setting is incorrect, change the TDM bus type by highlighting the TDM Bus Type (User Defined) parameter and selecting SCbus from the Value list. Then, click the Apply button.
3. Highlight the Primary Master FRU (User Defined) parameter.
4. From the Value list, select the board you would like to make the Primary Master.
5. Click the Apply button.
6. Highlight the Derive Primary Clock From (User Defined) parameter. Select the appropriate option from the Value list:
   • Internal Oscillator: the primary master derives clocking from its own internal circuitry.
   • FrontEnd_1: the primary master derives clocking from its own front end network interface (span 1 of a DualSpan board)

     Note: NOTE: The FrontEnd_1 value is only valid when the Primary Master FRU is a Springware board. This value cannot be used when the Primary Master FRU is a DM3 board.

   • FrontEnd_2: the primary master derives clocking from its own front end network interface (span 2 of a DualSpan board)

     Note: The FrontEnd_2 value is only valid when the Primary Master FRU is a Springware board. This value cannot be used when the Primary Master FRU is a DM3 board.

   Note: NETREF_1 and NETREF_2 values are not applicable to SCbus mode systems.

7. Click the OK button. This will apply the Derive Primary Clock From (User Defined) parameter modification and return to the DCM main window.

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