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CobraNet

Clocking Modes

1. INTRODUCTION

In most cases, a CobraNet

system is used with its default audio clocking mode (0x00). This allows automatic syn-

chronization of audio clocks network wide. However, the clocking circuitry of a CobraNet device can be configured

to operate in a number of ways that are specified by the values written to the syncConductorClock and syncPerform-

erClock Management Interface (MI) variables. These two MI variables are used independently to set the clocking

mode of an interface depending on whether it is operating as a Conductor or a Performer. These variables can be

set by using SNMP or the Host Management Interface (HMI).

Please see the CobraNet Programmer's Reference Manual

and the CobraNet Hardware User's Manual

for more in-

formation on the variables, SNMP, and the Host Management Interface.

2. IMPORTANT CONCEPTS REGARDING CobraNet CLOCKING

All devices in a CobraNet network must operate within the same clock domain. It is therefore a requirement that,

regardless of clock mode, all audio clocks on the network should be derived from the same master clock to ensure

that they remain synchronized. This is accomplished automatically when using the default clock mode, 0x00, and

when any digital devices attached to the CobraNet interface receive their audio clocks from the CobraNet interface.

• Any CobraNet interface that uses one of the external clocking modes must use external clocks that are syn-

chronous with the network audio clock.

• A digital audio device that does not receive its audio clocks from the CobraNet interface must be connected

to the CobraNet interface using a sample rate converter. For instance, all digital audio devices connected

to CobraNet devices must be in the same audio clock domain as the CobraNet network.

• Any clock mode that uses the external word clock (REFCLK_IN) will not work unless the REFCLK_IN pin is

first enabled by clearing the second bit (bit 1) of the syncBuddyLinkControl MI variable.

3. CORE CLOCK CIRCUITRY OF A CobraNet INTERFACE

The core clock circuitry of a CobraNet interface is depicted in Figures 1 and 2. Note that not all inputs and outputs

to the clock module are used at the same time in all modes. Operation of the circuitry, and activity on each path, are

dependent on the clock mode selected. These different clocking modes can be used in many ways, depending on

the requirements of a particular application. Common usage of the different modes is described in this document.

The user-available external clock connections are REFCLK, MCLK_IN, MCLK_OUT, FS1, and SCLK. The other

connections are internal to the interface and utilized by the interface's firmware in response to the particular mode

in use.

The five audio clock modes are:

• 0x00 - Internal (Normal Default Mode)

• 0x10 - Internal with External Sample Synchronization

• 0x01 - External Word Clock

• 0x04 - External Master Clock

• 0x14 - External Master Clock with External Sample Synchronization

AN312

MAY ‘08

AN312REV2

1 2 3 4 5 6 ... 13 14

Inhaltsverzeichnis

Seite 1 - Clocking Modes

Seite 2 - 2 AN312REV2

10 AN312REV2AN312Figure 16. 0x14 Mode Typical Connection (Master and Reference Clock Supplied to Slave Interfaces within Same Chassis when Using CM-1

Seite 3 - 3.1 CobraNet Clock Modes

AN312REV2 11AN3123.1.6 0x14 Mode for CM-2/CS1810xx/CS4961xx-Based DevicesNote: The 0x14 clock mode only works with devices running Rev. 2.11.6 firmwar

Seite 4

12 AN312REV2AN3124. USING 0x10 MODE WITH CS1810XX, CS4961XX OR CM-20x10 Mode is used when the designer wishes to synchronize the CobraNet clocks with

Seite 5

AN312REV2 13AN3126. REVISION HISTORYRelease ChangesRevision 1 Initial Release.Revision 2 Added more detail to Figures 18 and 19. Clarified language in

Seite 6 - 6 AN312REV2

14 AN312REV2AN312Contacting Cirrus Logic SupportFor all product questions and inquiries, contact a Cirrus Logic Sales Representative. To find the one

Seite 7

2 AN312REV2AN312Figure 1. - CobraNet Clock Circuit for CM-1 ModuleFigure 2. CobraNet Clock Circuit for CM-2 Module and SemiconductorsBeat ReceivedVC

Seite 8 - 8 AN312REV2

AN312REV2 3AN3123.1 CobraNet Clock ModesThis section describes each of the CobraNet clock modes.3.1.1 0x00 Mode - Internal Mode (Default)The 0x00 Mode

Seite 9 - 3.1.5.1 0x14 Mode for CM-1

4 AN312REV2AN312Figure 5. Clock Circuit as Used by Mode 0x00 with CM-2 and Semiconductors3.1.2 0x10 Mode - Internal Mode with External Sample Synchro

Seite 10 - 10 AN312REV2

AN312REV2 5AN3123.1.3 0x01 Mode - External Word ClockExternal Word Clock Mode allows synchronization of all CobraNet clocks with an externally supplie

Seite 11

6 AN312REV2AN312Figure 9. 0x01 Mode Typical Connection - Synchronization of All Nodes Note: All nodes should be on house synch.Figure 10. Mode 0x01

Seite 12 - 5. REFERENCES

AN312REV2 7AN312Figure 11. Clock Circuit as Used by Mode 0x01 with CM-2 and Semiconductors3.1.4 0x04 Mode - External Master ClockIn External Master C

Seite 13 - 6. REVISION HISTORY

8 AN312REV2AN312Figure 13. Clock Circuit as Used by Mode 0x04 with CM-1 ModuleFigure 14. Clock Circuit as Used by Mode 0x04 with CM-2 and Semiconduc

Seite 14 - 14 AN312REV2

AN312REV2 9AN3123.1.5 0x14 Mode - External Master Clock with External Sample Clock SynchronizationNote: This mode operates differently depending on us

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