CS61575-IP1 datasheet(16/44 Pages) CIRRUS

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Remote Loopback

Remote loopback is selected by taking RLOOP,

pin 26, high or by setting the RLOOP register bit

via the serial interface.

In remote loopback, the recovered clock and data

input on RTIP and RRING are sent through the

jitter attenuator and back out on the line via TTIP

and TRING. Selecting remote loopback overrides

any TAOS request (see Table 7). The recovered

incoming signals are also sent to RCLK, RPOS

and RNEG (or RDATA). Simultaneous selection

of local and remote loopback modes is not valid

(see Reset).

In the Extended Hardware Mode the transmitted

data is looped before the AMI/B8ZS/HDB3 en-

coder/decoder during remote loopback so that the

transmitted signal matches the received signal,

even in the presence of received bipolar viola-

tions. Data output on RDATA is decoded,

however, if RCODE is low.

Driver Performance Monitor

To aid in early detection and easy isolation of

non-functioning links, the IC is able to monitor

transmit drive performance and report when the

driver is no longer operational. This feature can

be used to monitor either the device’s perform-

ance or the performance of a neighboring driver.

The driver performance monitor indicator is nor-

mally low, and goes high upon detecting a driver

failure.

The driver performance monitor consists of an ac-

tivity detector that monitors the transmitted signal

when MTIP is connected to TTIP and MRING is

connected to TRING. DPM will go high if the

absolute difference between MTIP and MRING

does not transition above or below a threshold

level within a time-out period. In the Host Mode,

DPM is available from both the register and pin

11.

Whenever more than one line interface IC resides

on the same circuit board, the effectiveness of the

driver performance monitor can be maximized by

having each IC monitor performance of a neigh-

boring IC, rather than having it monitor its own

performance. Note that a CS61574A or CS61575

can not be used to monitor a CS61574 due to out-

put stage differences.

Line Code Encoder/Decoder

In the Extended Hardware Mode, three line codes

are available: AMI, B8ZS and HDB3. The input

to the encoder is TDATA. The outputs from the

decoder are RDATA and BPV (Bipolar Violation

Strobe). The encoder and decoder are selected

using the LEN2, LEN1, LEN0, TCODE and

RCODE pins as shown in Table 8.

LEN 2/1/0

000

010-111

TCODE

(Transmit

Encoder

Selection)

LOW

HDB3

Encoder

B8ZS

Encoder

HIGH

AMI

Encoder

RCODE

(Receiver

Decoder

Selection)

LOW

HDB3

Decoder

B8ZS

Decoder

HIGH

AMI

Decoder

Table 8. Encoder/Decoder Selection

RLOOP

Input

Signal

TAOS

Input

Signal

Source of

Data for

TTIP & TRING

Source of

Clock for

TTIP & TRING

TDATA

TCLK

all 1s

TCLK

RTIP & RRING RTIP & RRING (RCLK)

Notes: 1. X = Don’t care. The identified All Ones Select

input is ignored when the indicated loopback

is in effect.

2. Logic 1 indicates that Loopback or All Ones

option is selected.

Table 7. Interaction of RLOOP with TAOS

CS61574A CS61575

DS154F2

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