Maxim Integrated DS33R11 - Manual (Page 63)

DS33R11 Ethernet Mapper with Integrated T1/E1/J1 Transceiver
63 of 344
9.16.1 Receive Data Interface
9.16.1.1 Receive Pattern Detection
The Receive BERT receives only the payload data and synchronizes the receive pattern generator to the incoming
pattern. The receive pattern generator is a 32-bit shift register that shifts data from the least significant bit (LSB) or
bit 1 to the most significant bit (MSB) or bit 32. The input to bit 1 is the feedback. For a PRBS pattern (generating
polynomial x
n + x y + 1), the feedback is an XOR of bit n and bit y. For a repetitive pattern (length n), the feedback is
bit n. The values for n and y are individually programmable (1 to 32). The output of the receive pattern generator is
the feedback. If QRSS is enabled, the feedback is an XOR of bits 17 and 20, and the output is forced to one if the
next 14 bits are all zeros. QRSS is programmable (on or off). For PRBS and QRSS patterns, the feedback is
forced to one if bits 1 through 31 are all zeros. Depending on the type of pattern programmed, pattern detection
performs either PRBS synchronization or repetitive pattern synchronization.
9.16.1.2 PRBS Synchronization
PRBS synchronization synchronizes the receive pattern generator to the incoming PRBS or QRSS pattern. The
receive pattern generator is synchronized by loading 32 data stream bits into the receive pattern generator, and
then checking the next 32 data stream bits. Synchronization is achieved if all 32 bits match the incoming pattern. If
at least is incoming bits in the current 64-bit window do not match the receive pattern generator, automatic pattern
resynchronization is initiated. Automatic pattern resynchronization can be disabled.
Figure 9-9. PRBS Synchronization State Diagram
Sync
Load Verify
1 bit error
32 bits loaded
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