DS21Q58L【PDF 33/74 页】IC TXRX E1 QUAD 3.3V 100-LQFP

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DS21Q58 E1 Quad Transceiver

39 of 74

13.

PRBS GENERATION AND DETECTION

The DS21Q58 can transmit and receive the 2

15 - 1 PRBS pattern. This PRBS pattern complies with ITU-T O.151

specifications. The PRBS pattern can be unframed (in all 256 bits of the frame), framed (in all time slots except

TS0), or in any single time slot. Register CCR5 contains the control bits for configuring the transmit and receives

PRBS functions. See Table 13-1 and Table 13-2 for selecting the transmit and receive modes of operation. In

transmit and receive mode 1 operation, the transmit- and receive-channel monitor-select bits of registers CCR3

and CCR4 have an alternate use. When this mode is selected, these bits determine which time slot transmits

and/or receives the PRBS pattern.

SR2.0 indicates when the receiver has synchronized to the PRBS pattern. The PRBS synchronizer remains in sync

until it experiences six or more bit errors within a 64-bit span. Choosing any receive mode other than NORMAL

causes the 16-bit E-bit error counter—EBCR1 and EBCR2—to be reconfigured for counting PRBS errors.

User-definable outputs OUTA or OUTB can be configured to output a pulse for every bit error received. See

Section 20 and Table 20-1 for details. This signal can be used with external circuitry to keep track of bit-error rates

during PRBS testing. Once synchronized, any bit errors received cause a positive-going pulse, synchronous with

RCLK.

Table 13-1. Transmit PRBS Mode Select

TPRBS1

(CCR5.3)

TPBRS0

(CCR5.2)

MODE

Mode 0: Normal (PRBS disabled)

Mode 1: PRBS in TSx. PRBS pattern is transmitted in a single time slot (TS). In this mode, the

transmit-channel monitor-select bits in register CCR3 are used to select a time slot in which to

transmit the PRBS pattern.

Mode 2: PRBS in all but TS0. PRBS pattern is transmitted in time slots 1 through 31.

Mode 3: PRBS unframed. PRBS pattern is transmitted in all time slots.

Table 13-2. Receive PRBS Mode Select

RPRBS1

(CCR5.1)

RPBRS0

(CCR5.0)

MODE

Mode 0: Normal (PRBS disabled)

Mode 1: PRBS in TSx. PRBS pattern is received in a single time slot (TS). In this mode, the

receive-channel monitor-select bits in register CCR4 are used to select a time slot in which to

receive the PRBS pattern.

Mode 2: PRBS in all but TS0. PRBS pattern is received in time slots 1 through 31.

Mode 3: PRBS unframed. PRBS pattern is received in all time slots.

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