Preliminary Information
ISO-CMOS MT8977
False Candidate
Hunt Mode
False
Candidate
Forced
Reframe
Candidate
Out of
Sync.
False
Candidate
Verify
Candidate
Candidate
CRC
Check
*
Candidate
In sync
Maintenance
Valid Candidate
Valid Candidate
New Frame Position
Resync
Receiver
* Note: Only when in ESF mode and CRC
option is enabled.
Figure 9 - Off-Line Framer State Diagram
discovered. It is, therefore, possible that the device
may not synchronize at all in the presence of PCM
code sequences (e.g., sequences generated by
some types of test signals), which contain mimics of
the terminal framing pattern.
repositions the receive circuit only when it has
detected a valid frame position. When the framer
exits maintenance mode the receive counters remain
where they are until the framer has found a new
frame position. This means that if the user forces a
reframe when the device was really in the right
place, there will not be any disturbance in the circuit
because the framer has no effect on the receiver
Setting CRC/MIMIC bit high will force the framer to
synchronize to the first terminal framing pattern
detected. In standard D3/D4 applications, the user’s
system software should monitor the multiframe
synchronization state indicated by bit 3 in Master
Status Word 1. Failure of the device to achieve
multiframe synchronization within 4.5ms of terminal
frame synchronization, is an indication that the
device has framed up to a terminal framing pattern
mimic and should be forced to reframe.
until it has found synchronization.
The out of
synchronization criterion can be controlled by bit 0 in
Master Control Word 2. This bit changes the out of
frame conditions for the maintenance state.
One of the main features of the framer is that it
performs its function "off line". That is, the framer
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