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IDT82V2041E
SINGLE CHANNEL T1/E1/J1 SHORT HAUL LINE INTERFACE UNIT
Functional Description
28
December 9, 2005
3.7
TRANSMIT AND DETECT INTERNAL PATTERNS
The internal patterns (All Ones, All Zeros, PRBS/QRSS pattern and
Activate/Deactivate Loopback Code) will be generated and detected by
IDT82V2041E. TCLK is used as the reference clock by default. MCLK can
also be used as the reference clock by setting the PATT_CLK bit (MAINT0,
0DH) to ‘1’.
If the PATT_CLK bit (MAINT0, 0DH) is set to ‘0’ and the PATT[1:0] bits
(MAINT0,0DH)aresetto‘00’,thetransmitpathwilloperateinnormalmode.
When the chip is configured by hardware, the transmit path will operate
3.7.1
TRANSMIT ALL ONES
In transmit direction, the All Ones data can be inserted into the data
streamwhenthePATT[1:0]bits(MAINT0,0DH)aresetto‘01’.Thetransmit
data stream is output from TTIP/TRING. In this case, either TCLK or MCLK
can be used as the transmit clock, as selected by the PATT_CLK bit
(MAINT0, 0DH).
Inhardwarecontrolmode,theAllOnesdatacanbeinsertedintothedata
stream in transmit direction by setting PATT[1:0] pins to ‘01’. Refer to
53.7.2
TRANSMIT ALL ZEROS
If the PATT_CLK bit (MAINT0, 0DH) is set to ‘1’, the All Zeros will be
inserted into the transmit data stream when the PATT[1:0] bits (MAINT0,
0DH) are set to ‘00’.
3.7.3
PRBS/QRSS GENERATION AND DETECTION
A PRBS/QRSS will be generated in the transmit direction and detected
in the receive direction by IDT82V2041E. The QRSS is 220-1 for T1/J1
applications and the PRBS is 215-1 for E1 applications, with maximum zero
restrictions according to AT&T TR62411 and ITU-T O.151.
When the PATT[1:0] bits (MAINT0, 0DH) are set to ‘10’, the PRBS/
QRSS pattern will be inserted into the transmit data stream with the MSB
first. The PRBS/QRSS pattern will be transmitted directly or invertedly.
In hardware control mode, the PRBS data will be generated in the trans-
mitdirectionandinsertedintothetransmitdatastreambysettingPATT[1:0]
The PRBS/QRSS in the received data stream will be monitored. If the
PRBS/QRSS has reached synchronization status, the PRBS_S bit
(STAT0, 17H) will be set to ‘1’, even in the presence of a logic error rate less
than or equal to 10-1. The criteria for setting/clearing the PRBS_S bit are
PRBS data canbe inverted throughsetting the PRBS_INVbit(MAINT0,
0DH).
Any change of PRBS_S bit will be captured by PRBS_IS bit (INTS0,
19H). The PRBS_IES bit (INTES, 16H) can be used to determine whether
the ‘0’ to ‘1’ change of PRBS_S bit will be captured by the PRBS_IS bit or
any changes of PRBS_S bit will be captured by the PRBS_IS bit. When the
PRBS_IS bit is ‘1’, an interruptwill be generated if the PRBS_IM bit (INTM0,
14H) is set to ‘1’.
The received PRBS/QRSS logic errors can be counted in a 16-bit
counter if the ERR_SEL [1:0] bits (MAINT6, 13H) are set to ‘00’. Refer to
counter.
3.8
LOOPBACK
To facilitate testing and diagnosis, the IDT82V2041E provides four dif-
ferent loopback configurations: Analog Loopback, Digital Loopback,
Remote Loopback and Inband Loopback.
3.8.1
ANALOG LOOPBACK
When the ALP bit (MAINT1, 0EH) is set to ‘1’, the chip is configured in
Analog Loopback mode. In this mode, the transmit signals are looped back
to the Receiver Internal Termination in the receive path then output from
RCLK, RD, RDP/RDN. At the same time, the transmit signals are still output
to TTIP/TRING in transmit direction. The all-ones pattern can be generated
during analog loopback.
Figure-13 shows the process.
3.8.2
DIGITAL LOOPBACK
When the DLP bit (MAINT1, 0EH) is set to ‘1’, the chip is configured in
Digital Loopback mode. In this mode, the transmit signals are looped back
to the jitter attenuator (if enabled) and decoder in receive path, then output
from RCLK, RD, RDP/RDN. At the same time, the transmit signals are still
output to TTIP/TRING in transmit direction.
Figure-14 shows the process.
Both Analog Loopback mode and Digital Loopback mode allow the
sending of the internal patterns (All Ones, All Zeros, PRBS, etc.) which will
overwrite the transmit signals. In this case, either TCLK or MCLK can be
used as the reference clock for internal patterns transmission.
In hardware control mode, Digital Loopback can be selected by setting
LP[1:0] pins to ‘10’.
3.8.3
REMOTE LOOPBACK
When the RLP bit (MAINT1, 0EH) is set to ‘1’, the chip is configured in
Remote Loopback mode. In this mode, the recovered clock and data output
from Clock and Data Recovery on the receive path is looped back to the
jitter attenuator (if enabled) and Waveform Shaper in transmit path.
Figure-Inhardwarecontrolmode,RemoteLoopbackcanbeselectedbysetting
LP[1:0] pins to ‘11’.
Table-16 Criteria for Setting/Clearing the PRBS_S Bit
PRBS/QRSS
Detection
6 or less than 6 bit errors detected in a 64 bits hopping win-
dow.
PRBS/QRSS
Missing
More than 6 bit errors detected in a 64 bits hopping window.