Cirrus Logic CS61884 - Manual (Page 28)

CS61884
28 DS485F3
During host mode operation, LOS is reported in the
LOS Status Monitor Register. Both the LOS pins
and the register bits reflect LOS status in host mode
operation. The LOS pins and status bits are set high
(indicating loss of signal) during reset, power-up,
or channel powered-down.
10.6 Alarm Indication Signal (AIS)
The CS61884 detects all ones alarm condition per
the relevant ANSI, ITU, and ETSI specifications.
In general, AIS is indicated when the one’s density
of the receive signal exceeds that dictated by the
relevant specification. This feature is only avail-
able in host mode (Refer to
LOS/AIS Mode En-
able Register (0Dh) (See Section 14.14 on
page 37)).
ANSI T1.231 AIS (T1/J1 Mode) - The AIS condi-
tion is declared when less than 9 zeros are received
within a sliding window of 8192 bits. This corre-
sponds to a ones density of 99.9% over a period of
5.3 ms. The AIS condition is cleared when nine or
more zeros are detected in a sliding window of
8192 bits.
ITU G.775 AIS (E1 Mode) - The AIS condition is
declared when less than 3 zeros are received within
two consecutive 512 bit windows. The AIS condi-
tion is cleared when 3 or more zeros are received in
two consecutive 512 bit windows.
ETSI 300 233 (E1 Mode) - The AIS condition is
declared when less than 3 zeros are received in a
512 bit window. The AIS condition is cleared when
a 512 bit window is received containing 3 or more
zeros.
11. JITTER ATTENUATOR
The CS61884 internal jitter attenuators can be
switched into either the receive or transmit paths.
Alternatively, it can be removed from both paths to
reduce the propagation delay.
During Hardware mode operation, the location of
the jitter attenuator for all eight channels are con-
trolled by the JASEL pin (Refer to Table 6 for pin
configurations). The jitter attenuator’s FIFO length
and corner frequency, can not be changed in hard-
ware mode. The FIFO length and corner frequency
are set to 32 bits and 1.25Hz for the E1 operational
modes and to 32 bits and 3.78Hz in the T1/J1 oper-
ational modes.
During host mode operation, the location of the jit-
ter attenuator for all eight channels are set by bits 0
and 1 in the
Global Control Register (0Fh) (See
Section 14.16 on page 38). The GLOBAL CON-
TROL REGISTER (0Fh) also configures the jitter
attenuator’s FIFO length (bit 3) and corner fre-
quency (bit 2).
The attenuator consists of a 64-bit FIFO, a narrow-
band monolithic PLL, and control logic. The jitter
attenuator requires no external crystal. Signal jitter
is absorbed in the FIFO which is designed to nei-
ther overflow nor underflow.
If overflow or underflow is imminent, the jitter
transfer function is altered to ensure that no bit-er-
rors occur. A configuration option is provided to
reduce the jitter attenuator FIFO length from 64
bits to 32 bits in order to reduce propagation delay.
The jitter attenuator -3 dB knee frequency depends
on the settings of the Jitter Attenuator FIFO length
and the Jitter Attenuator Corner Frequency bits 2
and 3, in the
Global Control Register (0Fh) (See
Section 14.16 on page 38)). Setting the lowest cor-
ner frequency guarantees jitter attenuation compli-
ance to European specifications TBR 12/13 and
ETSI ETS 300 011 in E1 mode. The jitter attenua-
tor is also compliant with ITU-T G.735, G.742,
G.783 and AT&T Pub. 62411 (Refer to
Figure 19
on page 58 and Figure 20 on page 58 ).
Table 6. Jitter Attenuator Configurations
PIN STATE JITTER ATTENUATOR POSITON
LOW Transmit Path
HIGH Receive Path
OPEN Disabled