Data Sheet T7296 DS3/STS-1/E3
January 1997 Integrated Line Transmitter
5
Lucent Technologies Inc.
Overview
(continued)
System Description
B3ZS/HDB3 Encoder
Data to be transmitted is input to the encoder block to
be encoded either in B3ZS or HDB3 as determined by
the state of the DS3, STS-1/
E3
pin. Input data format
can be unipolar or binary. For binary signals, TPDATA
and TNDATA need to be connected together externally.
The line code used f or DS3 is B3ZS. In this mode, each
block of three consecutive zeros is removed and
replaced by one of tw o codes that contain bipolar viola-
tions. These replacement codes are B0V and 00V,
where B indicates a pulse conforming with the bipolar
rule, and V represents a pulse violating the rule. The
choice of these codes is made such that an odd num-
ber of B pulses will be transmitted between consecutiv e
bipolar violation (BPV) pulses. For E3 format, the line
code is HDB3. The encoding rule of HDB3 is similar to
B3ZS except that the number of consecutive zeros is
increased to four before a code replacement can take
place. The replacement codes in this case are 000V
and B00V.
STS-1 operation is achieved by placing the part in the
DS3 mode and using 51.84 MHz clocks. Logic opera-
tion for STS-1 is the same for DS3.
Transmit All 1s Select
Setting TAOS high causes contin uous AMI encoded 1s
to be transmitted to the line. In this mode, input
TPDATA and TNDATA are ignored. If remote loopback
(RLOOP) is set high, any TAOS request is ignored.
Remote Loopback
Setting RLOOP high causes received RPDATA and
RNDATA to be transmitted to the line through TTIP and
TRING. The data rate is determined by RCLK. In this
mode, TPDATA and TNDATA are ignored.
Local Loopback
Setting LLOOP high causes TPDATA and TNDATA to
go through both the encoder and the decoder. In this
mode, the signals transmitted on RCLKO, RPOS, and
RNEG correspond to those received on TCLK,
TPDATA, and TNDATA, respectively. TPDATA and
TNDATA are transmitted to the line unless overridden
by a TAOS request. Setting both RLOOP and LLOOP
high simultaneously is not permitted.
B3ZS/HDB3 Decoder
The decoder block is included to perform B3ZS or
HDB3 decoding as determined by the state of the DS3,
STS-1/
E3
pin. In the B3ZS format, the decoder detects
both B0V and 00V codes and replaces them with 000
data. If HDB3 decoding is selected by setting the DS3,
STS-1/
E3
pin low, the B00V and 000V codes are
detected and replaced with the 0000 code. In both
cases, bipolar violation and coding errors that do not
conform to the coding scheme are detected and indi-
cated at the BPV output pin.
Decoder Disable
For testing purposes and in applications where the
decoder needs to be bypassed, the decoder can be
disabled by setting DECODIS high. In this mode, all
bipolar violation pulses are indicated at the BPV pin.
Bipolar Violation Detection
The BPV pin goes high for one bit period when a code
error or a bipolar violation not corresponding to the
appropriate coding rule is detected on the RPDATA/
RNDATA signal. The violation pulse is always removed
from the decoder outputs RPOS/RNEG when DECO-
DIS is set low.
Pulse Shaper
The pulse shaper circuit uses a combination of filters
and slew-r ate control techniques to preshape the pulse
to be transmitted to the line. The amplitude of the tr ans-
mit pulse can be adjusted by using the TXLEV (tr ansmit
level) pin. When the distance to the cross connect
exceeds 120 ft., TXLEV should be set high. When the
distance is less than 120 ft., TXLEV should be set low.
Setting TXLEV high enab les the transmitter to send out
a nominal 1.0 V peak pulse. Setting TXLEV low
enables the transmitter to send out a nominal 850 mV
peak pulse. The state of the TXLEV pin has no effect
on E3 operation.
Driver Monitor
Using TTIP and TRING as inputs, the driver monitor
detects driver failure by monitoring the activities at
MTIP and MRING. If no signal is detected on these
pins for 128
±
32 TCLK cycles, DMO is set high until
the next AMI signal is detected.