XRT74L73 Datasheet, PDF (148/488 Pages) Exar Corporation – 3 CHANNEL, ATM UNI/PPP DS3/E3 FRAMING CONTROLLER

XRT74L73
3 CHANNEL, ATM UNI/PPP DS3/E3 FRAMING CONTROLLER
REV. P1.0.1
PRELIMINARY
in these comparison operations is more clearly de-
fined in Table 26 , on following page.
TABLE 26: ILLUSTRATION OF THE ROLE OF THE “RXCP USER CELL FILTER PATTERN HEADER BYTE” REGISTER
AND THE “RXCP USER CELL FILTER MASK HEADER BYTE” REGISTER.
Content of Header Byte-1 (of Incoming User Cell)
BIT 7
BIT 6
BIT 5
BIT 4
1
0
1
0
BIT 3
0
BIT 2
1
BIT 1
0
BIT 0
1
Content of “RxCP User Cell Filter Mask Header Byte-1 Register
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
1
1
1
1
0
BIT 2
0
BIT 1
0
BIT 0
0
Content of “RxCP User Cell Filter Pattern Header Byte-1 Register
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
1
1
1
1
0
BIT 2
0
BIT 1
0
BIT 0
0
Comments
BIT 7
BIT 6
BIT 5
BIT 4
Comparison is Forced (by the “1s” in the RxCP User Cell Filter
Mask Header Byte-1 Register)
BIT 3
Don’t Care
BIT 2
Don’t Care
BIT 1
Don’t Care
BIT 0
Don’t Care
Resulting “User Cell Fiilter” Pattern for Header Byte-1
BIT 7
BIT 6
BIT 5
BIT 4
1
0
1
0
BIT 3
x
BIT 2
x
BIT 1
x
BIT 0
x
Based upon these register settings, any cell containing
values in the range of A0h–AFh are considered to be
matching, at the first byte. This cell will be subjected to
three (3) more tests (e.g., one for each of the remain-
ing header bytes.)
After all of these comparison tests have been
performed, a given User cell will be deemed either
“matching” or “not matching” the settings of the User
Cell Filter. Once the cell has been classified into one
of these two categories, its disposition (or fate) is
dependent upon the content of bit-field 5 (User Cell
Filter Discard) within the “RxCP Additional Configura-
tion Register (Address = 4Dh). If this bit-field is ‘0’,
then only-matching cells will be retained, and written
into the RxFIFO. All remaining User Cells will be
discarded. Conversely, it this bit-field is ‘1’, then only
‘non-matching’ User Cells will be retained and written
to the RxFIFO. All ‘matching’ User Cells will be
discarded.
The bit-formats of the 8 registers that define the User
Cell Filtering criteria are presented below.
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