DS2148 datasheet(45/75 Pages) DALLAS

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DS2148/Q48

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8.2.3 Analog Loopback (ALB)

Setting ALB (CCR6.4) to a one puts the DS2148 in Analog Loop Back. Signals at TTIP and TRING will

be internally connected to RTIP and RRING. The incoming signals at RTIP and RRING will be ignored.

The signals at TTIP and TRING will be transmitted as normal. (See Figure 3-1.)

8.2.4 Dual Loopback (DLB)

Setting both CCR6.7 and CCR6.6 to a one, LLB and RLB respectively, puts the DS2148 into dual

loopback operation. The TCLK and TPOS/TNEG signals will be looped back through the jitter

attenuator (if enabled) and output at RCLK and RPOS/RNEG. Clock and data recovered from RTIP and

RRING will be looped back to the transmit-side and output at TTIP and TRING. This mode of operation

is not available when implementing hardware operation. (See Figure 3-1.)

8.3

PRBS Generation and Detection

Setting TPRBSE (CCR3.4) = 1 enables the DS2148 to transmit a 215-1 (E1) or a 220-1 (T1) Pseudo

Random Bit Sequence (PRBS) depending on the ETS bit setting in CCR1.7. The receive-side of the

DS2148 will always search for these PRBS patterns independent of CCR3.4. The PRBS Bit Error Output

(PBEO) will remain high until the receiver has synchronized to one of the two patterns (64 bits received

without an error) at which time PBEO will go low and the PRBSD bit in the status register (SR) will be

set. Once synchronized, any bit errors received will cause a positive going pulse at PBEO, synchronous

with RCLK. This output can be used with external circuitry to keep track of bit error rates during the

PRBS testing. Setting CCR6.0 (ECRS) = 1 will allow the PRBS errors to be accumulated in the 16-bit

counter in registers ECR1 and ECR2. The PRBS synchronizer will remain in sync until it experiences 6

bit errors or more within a 64 bit span. Both PRBS patterns comply with the ITU-T O.151 specifications.

8.4

Error Counter

Error Count Register 1 (ECR1) is the most significant word and ECR2 is the least significant word of a

user-selectable 16-bit counter that records incoming errors including BiPolar Violations (BPV), Code

Violations (CV), Excessive Zero violations (EXZ) and/or PRBS Errors. See Table 8-3 and Table 8-4 and

Figure 3-2 for details.

DEFINITION OF RECEIVED ERRORS Table 8-3

ERROR

E1 OR T1

DEFINITION OF RECEIVED ERRORS

BPV

E1/T1

Two consecutive marks with the same polarity. Will ignore BPVs due to

HDB3 and B8ZS zero suppression when CCR2.3 = 0. Typically used with

AMI coding (CCR2.3 = 1). ITU-T O.161.

When HDB3 is enabled (CCR2.3 = 0) and the receiver detects two

consecutive BPVs with the same polarity. ITU-T O.161.

EXZ

When four or more consecutive zeros are detected.

EXZ

When receiving AMI coded signals (CCR2.3 = 1), detection of 16 or more

zeros or a BPV. ANSI T1.403 1999.

When receiving B8ZS coded signals (CCR2.3 = 0), detection of 8 or more

zeros or a BPV. ANSI T1.403 1999.

PRBS

E1/T1

A bit error in a received PRBS pattern. See Section 8.3 for details.

ITU-T O.151.

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