CS61304A Cirrus Logic, Inc., CS61304A Datasheet - Page 13

• Manufacturer Part Number: CS61304A
• Description: T1-E1 Line Interface Unit for CPE-ISDN PRI
• Manufacturer: Cirrus Logic, Inc.

X = Don’t care
Loss of Signal
The receiver will indicate loss of signal after
power-up, reset or upon receiving 175 consecu-
tive zeros. A digital counter counts received
zeros, based on RCLK cycles. A zero is received
when the RTIP and RRING inputs are below the
input comparator slicing threshold level estab-
lished by the peak detector. After the signal is
removed for a period of time the data slicing
th resho ld level decays to ap proximately
300 mV
The receiver reports loss of signal by setting the
Loss of Signal pin, LOS, high. If the serial inter-
face is used, the LOS bit will be set and an
interrupt will be issued on INT (unless disabled).
LOS will return low (asserting the INT pin again
in Host Mode) upon receipt of 3 ones in 32 bit
periods with no more than 15 consecutive zeros.
Note that in the Host Mode, LOS is simultane-
ously available from both the register and pin 12.
RPOS/RNEG or RDATA are forced low during
LOS unless the jitter attenuator is disabled. (See
"Jitter Attenuator")
If ACLKI is present during the LOS state, ACLKI
is switched into the input of the jitter attenuator,
resulting in RCLK matching the frequency of
ACLKI. The jitter attenuator buffers any instanta-
neous changes in phase between the last
DS156PP2
(>(V+) - 0.2V)
(>(V+) - 0.2V)
MIDDLE
(<0.2V)
MODE
(pin 5)
(2.5V)
HIGH
HIGH
LOW
Table 5. Data Output/Clock Relationship
peak
.
(pin 28)
CLKE
HIGH
LOW
X
X
RDATA
RNEG
RNEG
RNEG
RPOS
RPOS
RPOS
DATA
SDO
SDO
CLOCK
RCLK
RCLK
RCLK
RCLK
RCLK
RCLK
RCLK
SCLK
SCLK
for Valid Data
Clock Edge
Falling
Falling
Falling
Falling
Rising
Rising
Rising
Rising
Rising
recovered clock and the ACLKI reference clock.
This means that RCLK will smoothly transition
to the new frequency. If ACLKI is not present,
then the crystal oscillator of the jitter attenuator is
forced to its center frequency. Table 6 shows the
status of RCLK upon LOS.
Jitter Attenuator
The jitter attenuator reduces wander and jitter in
the recovered clock signal. It consists of a FIFO,
a crystal oscillator, a set of load capacitors for the
crystal, and control logic. The jitter attenuator ex-
ceeds the jitter attenuation requirements of
Publications 43802 and REC. G.742. A typical
jitter attenuation curve is shown in Figure 12. The
CS61304A fully meets AT&T 62411 jitter attenu-
ation requirements.
present?
Crystal
10
20
30
40
50
60
Yes
Yes
No
0
1
Figure 12. Typical Jitter Transfer Function
b) Maximum
Attunuation
Limit
present?
Table 6. RCLK Status at LOS
ACLKI
Yes
Yes
No
10
a) Minimum Attenuation Limit
ACLKI via the Jitter Attenuator
100
Frequency in Hz
Centered Crystal
Source of RCLK
62411 Requirements
Measured Performance
CS61304A
ACLKI
1 k
10 k
13