XRT74L73 Datasheet, PDF (78/488 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
BIT NUMBER
NAME
3-2
UTOPIA/POS-PHY Data
Bus Width[1:0]
TYPE
R/W
DESCRIPTION
UTOPIA/POS-PHY Data Bus Width[1:0]:
These READ/WRITE bit-fields permit the user to select the width
of the Transmit UTOPIA and POS-PHY Data Buses. The rela-
tionship between the contents of these bit-fields and the corre-
sponding widths of the Transmit UTOPIA and POS-PHY Data
Bus is tabulated below.
UTOPIA/POS-PHY
Data Bus
W id th [1 :0 ]
0
0
0
1
1
0
1
1
Corresponding
UTOPIA/POS-PHY
Data Bus Width
Not Valid
8 bits
16 bits
Not Valid
1-0
Cell Size[1:0]
Cell Size[1:0]:
These two READ/WRITE bit-fields permit the user to specify the
size of the ATM cell that will be handled by the Transmit UTOPIA
Interface blocks. The relationship between the contents of these
bit-fields and the corresponding Cell Sizes are tabulated below.
Cell Size[1:0] Resulting Cell Size (Bytes)
0
0
52 bytes
53 bytes (Only valid for
UTOPIA Level 1, and if the
0
1
UTOPIA Data Bus W idth is set
to 8 bits)
1
0
54 bytes (Only valid for
UTOPIA Levels 1 and 2)
1
1
56 bytes
NOTE: The user must bear in mind the UTOPIA Level and the
UTOPIA Data Bus width selected, when selecting the Cell Size.
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