Octal T1/E1/J1 Transceiver
—
LXT384
Datasheet
25
The AIS condition is cleared when, within two consecutive 512 bit periods, 3 or more zeros
are detected for each 512 bit period.
2.2.2.2
T1 Mode
ANSI T1.231 detection is employed.
The AIS condition is declared when less than 9 zeros are detected in any string of 8192 bits. This
corresponds to a 99.9% ones density over a period of 5.3ms.
The AIS condition is cleared when the received signal contains 9 or more zeros in any string of
8192 bits.
2.2.3
Receive Alarm Indication Signal (RAIS)
The receiver will generate all ones to RPOS and RNEG outputs upon LOS, when bit 6, RAISEN,
for Receive Alarm Indication Signal Enable, is set in the Global Control Register, GCR. This can
affect the AIS status by setting to one if the signal at RTIP and RRING is all zeroes, or be clearing
to zero if the signal at RTIP and RRING is all ones. Because of this, mask the AIS interrupt enable
bits before setting or resetting RAISEN. This will prevent inadvertent interrupts during
programming.
2.2.4
In Service Code Violation Monitoring
In unipolar I/O mode with HDB3/B8ZS decoding, the LXT384 reports bipolar violations on
RNEG/BPV for one RCLK period for every HDB3/B8ZS code violation that is not part of the zero
code substitution rules. In AMI mode, all bipolar violations (two consecutive pulses with the same
polarity) are reported at the BPV output.
2.3
Transmitter
The eight low power transmitters of the LXT384 are identical. Transmit data is clocked serially
into the device at TPOS/TNEG in the bipolar mode or at TDATA in the unipolar mode. The
transmit clock (TCLK) supplies the input synchronization. Unipolar I/O and HDB3/B8ZS/AMI
encoding/decoding is selected by pulling TNEG High for more than 16 consecutive TCLK clock
cycles. The transmitter samples TPOS/TNEG or TDATA inputs on the falling edge of TCLK. Refer
to the Test Specifications Section for MCLK and TCLK timing characteristics. If TCLK is not
supplied, the transmitter remains powered down and the TTIP/TRING outputs are held in a High Z
state. In addition, fast output tristatability is also available through the OE pin (all ports) and/or the
port
’
s OEx bit in the Output Enable Register (OER).
Zero suppression is available only in Unipolar Mode. The two zero-suppression types are B8ZS,
used in T1 environments, and HDB3, used in E1 environments. The scheme selected depends on
whether the device is set for T1 or E1 operation (determined by LEN2-0 pulse shaping settings).
The LXT384 also supports AMI line coding/decoding as shown in
Figure 5
. In Hardware mode,
AMI coding/decoding is selected by the CODEN pin. In host mode, AMI coding/decoding is
selected by bit 4 in the GCR (Global Control Register).