XRT74L74 Datasheet, PDF (161/498 Pages) Exar Corporation – 4 CHANNEL, ATM UNI/PPP DS3/E3 FRAMING CONTROLLER

PRELIMINARY
XRT74L74
4 CHANNEL, ATM UNI/PPP DS3/E3 FRAMING CONTROLLER
REV. P1.1.1
PMON Received Idle Cell Count—LSB (Address = 33h)
BIT 7
RO
0
BIT 6
RO
0
BIT 5
RO
0
BIT 4
BIT 3
RxIdle Cell Count—Low Byte
RO
RO
0
0
BIT 2
RO
0
BIT 1
RO
0
BIT 0
RO
0
The content of these registers are the number of Idle
Cells that have been detected, by the Receive Cell
Processor, since the last read of these registers.
These registers are reset upon read.
4.3.2.3.2 User Cell Filtering
The Receive Cell Processor can be configured to fil-
ter incoming user or OAM cells based upon the value
of their header bytes. The UNI provides the user with
three (3) options.
• Disable the User Cell Filter.
• Pass only those cells with header byte patterns
matching the settings of the User Cell Filter.
• Discard only those cells with header byte patterns
matching the settings of the User Cell Filter.
Each of these User-Cell Filtering Options are
discussed below.
Disable the User-Cell Filter
If the user disables the User-Cell Filter, within the
Receive Cell Processor, then all user cells (indepen-
dent of their header byte patterns) will be written into
the RxFIFO, within the Receive UTOPIA Interface
block.
RxCP Additional Configuration Register (Address = 4Dh)
BIT 7
BIT 6
Unused
RO
RO
BIT 5
User Cell Filter
Discard
R/W
BIT 4
User Cell Filter
Enable
R/W
BIT 3
BIT 2
Correction Threshold [1, 0]
R/W
R/W
BIT 1
Correction
Enable
R/W
BIT 0
Unused
RO
Writing a “1” to Bit 4 (User Cell Filter Enable) enables
the User Cell Filter. Whereas, writing a ‘0” to this bit-field
disables the User Cell Filter.
Enable the User Cell Filter
If the User Cell Filter is enabled, then the Receive
Cell Processor will be filtering user cells in one of two
possible manners.
1. Pass Only those cells with header bytes patterns
matching the User Cell Filter settings (e.g., the
contents of the “RxCP User Cell Filter Pattern
Header Byte” registers), or
2. Discard only those cells with header byte patterns
matching the User Cell Filter settings.
The User (or Assigned) cell filtering criteria is defined
based upon the contents of 8 read/write registers.
These eight registers are the four “RxCP User Cell Fil-
ter Pattern Header byte” registers and the four “RxCP
User Cell Filter Mask Header Byte” registers. In short,
when a user cell reaches the Receive Cell Processor,
the contents of each header byte of this cell (bytes 1
through 4), will be compared against the contents of
the corresponding “RxCP User Cell Filter Pattern
Header Byte” registers based upon constraints speci-
fied by the contents of the “RxCP User Cell Filter
Mask Header Byte” registers. The role of these registers
in “User Cell Filtering” is illustrated in the example
below.
Example—User Cell Filtering
For example, header byte 1 of a given incoming User
cell will be subjected to a bit-by-bit comparison to the
contents of the “RxCP User Cell Filter Pattern Header
Byte-1” register (Address = 58h). However, the con-
tents of the “RxCP User Cell Filter Mask Header
Byte-1” register (Address = 5Ch) also plays a role in
this comparison process. For example, if bit-field “0”
within the “RxCP User Cell Filter Mask Header Byte-1”
register contains a “1”, then the Receive Cell Processor
will perform the comparison operation between bit-field
“0” within the “RxCP User Cell Filter Pattern Header
Byte-1” register; and bit-field “0” within header byte 1
of the newly received User cell. Conversely, if bit-field
‘0’ within the “RxCP User Cell Filter Mask Header
Byte-1” register contains a ‘0’, then this comparison
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