CS61574A/75 Cirrus Logic, Inc., CS61574A/75 Datasheet - Page 16

• Manufacturer Part Number: CS61574A/75
• Description: T1/E1 Line Interface Unit for Stratum-4 applications
• Manufacturer: Cirrus Logic, Inc.

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).
Notes: 1. X = Don’t care. The identified All Ones Select
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-
16
RLOOP
Signal
Input
0
0
1
Table 7. Interaction of RLOOP with TAOS
2. Logic 1 indicates that Loopback or All Ones
input is ignored when the indicated loopback
is in effect.
option is selected.
Signal
TAOS
Input
X
0
1
RTIP & RRING RTIP & RRING (RCLK)
TTIP & TRING
Source of
Data for
TDATA
all 1s
TTIP & TRING
Source of
Clock for
TCLK
TCLK
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.
Selection)
Selection)
(Receiver
(Transmit
Decoder
Encoder
RCODE
TCODE
Table 8. Encoder/Decoder Selection
HIGH
HIGH
LOW
LOW
CS61574A CS61575
Decoder
Encoder
HDB3
HDB3
000
LEN 2/1/0
Encoder
Decoder
AMI
AMI
Decoder
Encoder
010-111
B8ZS
B8ZS
DS154F2