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DS21Q55

27. INTERLEAVED PCM BUS OPERATION

In many architectures, the PCM outputs of individual framers are combined into higher speed PCM buses to simplify transport across the system backplane. The DS21Q55 can be configured to allow PCM data to be multiplexed into higher speed buses eliminating external hardware, saving board space and cost. The DS21Q55 can be configured for channel or frame interleave.

The interleaved PCM bus option (IBO) supports three bus speeds. The 4.096MHz bus speed allows two PCM data streams to share a common bus. The 8.192MHz bus speed allows four PCM data streams to share a common bus. The 16.384MHz bus speed allows eight PCM data streams to share a common bus. See Figure 30-1 for an example of four transceivers sharing a common 8.192MHz PCM bus. The receive elastic stores of each transceiver must be enabled. Via the IBO register the user can configure each transceiver for a specific bus position. For all IBO bus configurations each transceiver is assigned an exclusive position in the high-speed PCM bus. The 8kHz frame sync can be generated from the system backplane or from the first device on the bus. All other devices on the bus must have their frame syncs configured as inputs. Relative to this common frame sync, the devices will await their turn to drive or sample the bus according to the settings of the DA0, DA1, and DA2 bits of the IBOC register.

27.1 Channel Interleave Mode

In channel interleave mode, data is output to the PCM data-out bus one channel at a time from each of the connected devices until all channels of frame n from each device has been placed on the bus. This mode can be used even when the DS21Q55s are operating asynchronous to each other. The elastic stores will manage slip conditions.

27.2 Frame Interleave Mode

In frame interleave mode, data is output to the PCM data-out bus one frame at a time from each of the devices. This mode is used only when all connected devices are operating in a synchronous fashion (all inbound T1 or E1 lines are synchronous) and are synchronous with the system clock (system clock derived from T1 or E1 line). In this mode, slip conditions are not allowed.

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Maxim DS21Q55 specifications Interleaved PCM BUS Operation, Channel Interleave Mode, Frame Interleave Mode