
XRT74L74
4 CHANNEL, ATM UNI/PPP DS3/E3 FRAMING CONTROLLER
REV. P1.1.1
PRELIMINARY
98
byte, and a stuff byte in the cell)
The selection is made by writing the appropriate data
to bit 3 (CellOf52 Bytes) within the UTOPIA Configu-
ration Register, as depicted below.
The following table specifies the relationship between
the value of this bit and the number of octets/cell that
the Transmit UTOPIA Interface block will process.
Note: This selection applies to both the Transmit UTOPIA
and Receive UTOPIA interface blocks. Additionally, the
shaded selection reflects the default condition upon power
up or reset.
3.1.2.1.3
Parity Checking and Handling of ATM
Cell Data received from the ATM Layer
Processor
The ATM Layer processor is expected to compute the
odd parity bit for all bytes or words that it intends to
write into the Transmit UTOPIA Interface block. The
ATM Layer processor is then expected to apply the
value of this parity bit to the TxUPrty input pin of the
UNI, while the corresponding byte (or word) is
present on the Transmit UTOPIA data bus. The Trans-
mit UTOPIA Interface block will independently com-
pute the odd parity of the contents on the Transmit
UTOPIA Data Bus. Afterwards, the Transmit UTOPIA
Interface block will compare its calculated value for
parity with that placed on the TxUPrty input pin (by
the ATM Layer processor). If these two values are
equal, then the byte (or word) of data will be pro-
cessed through the Transmit UTOPIA Interface block.
However, if these two parity values are not equal,
then the
“Detection of Parity Error (Transmit UTOPIA
Interface)” interrupt will occur, and the cell comprising
this errored byte (or word) will be (optionally) discard-
ed. The Transmit UTOPIA Interface block can be con-
figured to discard or retain this “errored” cell by writ-
ing the appropriate data to the Transmit UTOPIA In-
terrupt/Status Register (Address = 6Eh) as depicted
below.
If this bit is set to a “1”, then the Transmit UTOPIA In-
put Interface block will discard the errored cell. If this
bit-field to is set to “0”, then the Transmit UTOPIA In-
terface block will not discard the errored cell and this
cell will be written into the TxFIFO.
3.1.2.2
The TxFIFO Manager has the following responsibilities.
Monitoring the fill level of the TxFIFO, and providing
the appropriate level of Flow Control of data
Transmit UTOPIA FIFO Manager
UTOPIA Configuration Register: Address = 6Ah
B
IT
7
B
IT
6
B
IT
5
B
IT
4
B
IT
3
B
IT
2
B
IT
1
B
IT
0
Unused
Handshake Mode
M-PHY
CellOf52 Bytes
TFIFODepth[1, 0]
UtWidth16
RO
R/W
R/W
R/W
R/W
R/W
T
ABLE
4: T
HE
R
ELATIONSHIP
BETWEEN
THE
CONTENTS
OF
B
IT
3 (C
ELL
O
F
52B
YTES
)
WITHIN
THE
UTOPIA
C
ONFIGURATION
R
EGISTER
,
AND
THE
NUMBER
OF
OCTETS
PER
CELL
THAT
WILL
BE
PROCESSED
BY THE
T
RANSMIT
AND
R
ECEIVE
UTOPIA I
NTERFACE
BLOCKS
.
C
ELL
O
F
52 B
YTES
N
UMBER
OF
B
YTES
/C
ELLS
0
53 bytes when the UTOPIA Data Bus width is 8 bits.
54 bytes when the UTOPIA Data Bus width is 16 bits.
1
52 bytes, regardless of the configured width of the UTOPIA Data Bus
Transmit UTOPIA Interrupt/Status Register (Address = 6Eh)
B
IT
7
B
IT
6
B
IT
5
B
IT
4
B
IT
3
B
IT
2
B
IT
1
B
IT
0
TFIFO Reset
Discard
Upon PErr
TPerr IntEn
TFIFO
ErrIntEn
TCOCA
IntEn
TPErr IntStat
TFIFO”
OverInt Stat
TCOCA
IntStat
R/W
R/W
R/W
R/W
R/W
RUR
RUR
RUR