RELEASED
PM73123 AAL1GATOR-8
DATASHEET
PMC-2000097
ISSUE 2
8 LINK CES/DBCES AAL1 SAR
Table 6 Channel Status
CGC_LINE(4:0) Value
CGC_DOUT(3:0) Value
3
2
1
0
15
0
Line(3)
Line(2)
Line(1)
14
13
12
Channel(4)
Channel(3)
Channel(2)
Channel(1)
Underrun_h
0
0
0
underrun_l
0
0
0
0
0
0
0
9.3.3.4 Adaptive Status Output
The AAL1gator-8 provides the average buffer depth in units of bytes for an
external circuit to generate an adaptive clock. (If adap_filt_size is set to zero it
will provide the current buffer depth with no averaging). The general mechanism
is often termed “buffer centering”. A clock delta value is determined externally by
subtracting the nominal buffer depth (value of CDVT) from the actual buffer
depth. This delta value is then transformed into the frequency selection for an
external frequency synthesizer. The closed-loop action of this circuit causes the
delta value to find a center point. When the delta is above the center point, there
is too much data buffered and the frequency must be increased. When the delta
is below the center point, the frequency must be reduced.
The AAL1gator-8 implements a programmable weighted moving average
internally. However, if an alternative adaptive algorithm is desired then this
information can be processed externally. In High Speed mode, since an E3 or
DS3 clock cannot be internally synthesized, this information can be used for
external synthesis of an E3 or DS3 clock.
Table 7 below shows an example of the CGC Interface for adaptive data. In this
example the line number is 21, and the average buffer depth in units of bytes is
43. (For unstructured lines, the average buffer depth is given in units of bytes.
For structured lines, the average buffer depth is given in units of frames, ie,
buff_depth(4:0) should be ignored.) These values are encoded into the 6 data
words following the format shown.
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