DS3141 datasheet(20/88 Pages) DALLAS

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DS3141/DS3142/DS3143/DS3144 Single/Dual/Triple/Quad DS3/E3 Framers

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7.4 Error Insertion

Errors can be created in the transmit overhead and line coding for diagnostic purposes. These errors do not cause

any loss of data when created. The T3E3EIC error insertion register contains all the control bits to create errors.

The TMEI input pin can also be used to create errors.

7.5 Loopbacks

7.5.1 Line Loopback

The line loopback connects the incoming DS3/E3 data (RCLK, RPOS/RNRZ, and RNEG inputs) directly back to

the transmit side (TCLK, TPOS/TNRZ, and TNEG outputs). When this loopback is enabled, the incoming data

continues to pass through the receive framer block, but the output data from the transmit formatter is ignored. See

Figure 1-1 for a visual description of this loopback. Setting the LLB bit in the MC2 register activates the line

loopback.

7.5.2 Diagnostic Loopback

The diagnostic loopback sends the outgoing DS3/E3 data directly back to the receive side. When this loopback is

enabled, the incoming receive data at RCLK, RPOS, and RNEG is ignored. See Figure 1-1 for a visual description

of this loopback. During diagnostic loopback the device can simultaneously generate AIS at the TCLK, TPOS, and

TNEG outputs, while regular traffic is looped back to the receiver. This feature keeps the diagnostic signal that is

being looped back from disturbing downstream equipment. Setting the DLB bit in the MC2 register activates the

diagnostic loopback.

7.5.3 Payload Loopback

The payload loopback sends the DS3/E3 payload from the receive framer back to the transmit formatter. When this

loopback is enabled, the incoming receive data continues to be present on the RDAT pin, but the transmit data on

the TDAT pin is ignored. During payload loopback, the TSOF and TDEN signals are realigned to the receive frame,

and the signals at TOH and TOHEN are active and can still overwrite any bit position. See Figure 1-1 for a visual

description of this loopback. During payload loopback TSOF, TDEN, TOHEN, and TOH are aligned to the ROCLK

signal. When PLB and DLB are both set, diagnostic loopback takes precedence. Setting the PLB bit in the MC2

7.5.4 BERT and Loopback Interaction

Table 7-A describes how the payload bits move through the device with various combinations of BERT modes and

loopbacks active. The BERT mode is set in the BM[1:0] bits in the BCR1 register. The BERT is enabled when the

BENA bit is set in the BCR1 register. Table 7-B describes how the overhead bits move through the device with

various combinations of BERT modes and loopbacks active.

Table 7-A. BERT/Loopback Interaction—Payload Bits

CONFIGURATION BITS

BITS AT PAYLOAD BIT POSITIONS

DLB

LLB

PLB

BM [1:0]

From RPOS/RNEG To:

From TDAT To:

From BERT To:

BERT and RDAT

Not used

TPOS/TNEG

Not used

BERT and TPOS/TNEG

RDAT

Not used

TPOS/TNEG, BERT, and

RDAT

Not used

BERT and TPOS/TNEG

RDAT

TPOS/TNEG, RDAT, and

BERT

Not used

TPOS/TNEG

BERT

RDAT

TPOS/TNEG and RDAT

and BERT

Not used

RDAT and BERT

Not used

TPOS/TNEG

BERT

RDAT

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