Preliminary Information
MH89790B
framer, but is independent of the multiframe
synchronization. The CRC framer will not initiate a
search for CRC framing signal until frame alignment
synchronization is achieved. Once frame alignment
synchronization is acquired, the CRC framer must
find two framing signals in bit 1 of the non-frame
alignment signal. Upon detection of the second CRC
framing signal the MH89790B will immediately go
Input impedance seen by the transmission line is
about 75 ohms, (transformer ratio 1:1:1 with
center-tap grounded) as required by G.703 for
coaxial cable. Attenuation of the transmission line
shall not exceed 6dB (at 1024 kHz) and attenuation
characteristics shall be close to the “square root of
F”.
f
into CRC synchronization.
When maintenance
AF [dB] = AF [dB] *
ref
fref
feature is enabled (maint bit = 1) the CRC framer will
force a complete reframe of the device if CRC frame
synchronization is not found within 8 ms or more
than 914 CRC errors occur per second.
where:
AF - attenuation at frequency f in dB
AF - attenuation at frequency f
in dB (in this
ref
ref
Bipolar Line Receiver
case 6 dB)
The MH89790B receiver interfaces to the
transmission line through a pulse transformer which
splits the received AMI line signal into RxA and
f
-
reference frequency (in this case 1024
kHz)
ref
RxB.
These two signals are combined by an
f -
frequency in kHz
internal NAND gate to form a new signal, which
represents received data. The received data is
clocked into the chip on the falling edge of E2o.
Figure 28 shows the functional timing of the bipolar
receiver.
Input jitter tolerance of the MH89790B exceeds
minimum jitter tolerance as specified in CCITT I.431
and G.823 (see Figure 13).
out of
synchronization
No
search for frame
alignment
signal
Yes
No
verify bit 2 of non-
frame alignment
signal
# of consecutive incorrect
frame alignment signals = 3
Yes
No
verify second
occurrence of frame
alignment signal
time out > 8ms
Yes
frame synchroni-
zation acquired
No
find two CRC
search for
frame alignment
signals
multiframe align-
ment signal
number of CRC
errors > 914/s
Yes
Yes
multiframe synchro-
nization acquired
CRC synchronization
acquired
Yes
check for two errored
multiframe alignment
signals
Only if the
- - - - -
maintenance
option is
No
selected
Figure 12 - Synchronization State Diagram
4-201
MITEL [ MITEL NETWORKS CORPORATION ]
