cx29503 Mindspeed Technologies, cx29503 Datasheet - Page 61

• Manufacturer Part Number: cx29503
• Description: Cx29503 Broadband Access Multiplexer Data Sheet
• Manufacturer: Mindspeed Technologies

CX29503 Data Sheet
2.6.1.4
2.6.1.5
29503-DSH-002-B
DS3/E3 Smoothing Function
The DS3/E3 Smoothing function takes a 51.84 MHz bit stream with data enable that
corresponds to a DS3 or an E3 rate. This 51.84 MHz bit stream contains DS3/E3 data
based on their asynchronous mappings in a SONET/SDH signal. The DS3/E3
smoother generates a 51.84 MHz bit stream of redistributed (smoothed) DS3 or E3
data with a gapped data enable.
The data enable stream is used to gap the 51.84 MHz clock to generate a gapped
51.84 MHz clock for the DS3/E3 framers. The gapping requirement is such that
consecutive gaps are not allowed. The gapped 51.84 MHz clock and smoothed data
interface to the embedded DS3/E3 framers.
The DS3/E3 Smoothing function is implemented with a 256 × 1 FIFO. 128 bits are
allocated due to the maximum number of consecutive non-DS3 or non-E3 bits that
can be encountered and another 128 bits are allocated for pointer adjustments. The
FIFO is initialized at the half-full position.
For the DS3 case, the FIFO is read with the fast gapping sequence until the minimum
threshold is crossed at the end of the sequence. Once the minimum threshold is
crossed, the FIFO is read with the slow gapping sequence until the minimum threshold
is achieved at the end of the sequence. Thereafter, the fast sequence is again be used.
For the E3 case, the FIFO is read with 1 of 3 gapping sequences, according to the
FIFO fill level based on the following at the end of the preceding sequence:
An increment/decrement counter tracks the FIFO fill level.
FIFO overflows and underflows are detected. When detected, the overflow/underflow
status is latched for software read, and the FIFO is reset at the half-full position.
VT Extraction Control
The VT extraction control performs VT level pointer interpretations on each VT
present in the SPE envelope, which locates and processes the V1/V2 pointer bytes and
locates the first byte in the VT superframe. VT bytes and columns are counted so that
a point of reference is provided to the VT PM, DS1/E1 Demapping functions, and the
TSB Interface blocks.
This block detects new pointers without NDFs, and counts positive and negative
pointer justification operations as well as provides the current pointer value. The
CX29610 device also tracks these pointer operations.
fill level has increased (fast sequence)
fill level has stayed constant (nominal sequence)
fill level has decreased (slow sequence)
Mindspeed Technologies™
Preliminary Information
Functional Description
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