XRT74L73
3 CHANNEL, ATM UNI/PPP DS3/E3 FRAMING CONTROLLER
REV. P1.0.1
PRELIMINARY
95
Note: regarding Figure 9
1. The Transmit UTOPIA Data Bus is configured to be
16 bits wide. Hence, the data, which the ATM Layer
processor places on the Transmit UTOPIA Data
Bus, is expressed in terms of 16-bit words: W0–W26.
2. The Transmit UTOPIA Interface Block is configured to
handle 54 bytes/cell. Hence, Figure 9 illustrates the
ATM Layer processor writing 27 words (W0 through
W26) for each ATM cell.
3. The Transmit UTOPIA Interface Block is configured to
operate in the Cell-Level Handshaking mode.
Note: regarding Figure 10
1. The Transmit UTOPIA Data Bus is configured to be
16 bits wide. Hence, the data, which the ATM Layer
processor places on the Transmit UTOPIA Data
Bus, is expressed in terms of 16-bit words: W0–W26.
2. The Transmit UTOPIA Interface Block is configured to
handle 54 bytes/cell. Hence, Figure 10 illustrates the
ATM Layer processor writing 27 words (W0 through
W26) for each ATM cell.
3. The Transmit UTOPIA Interface Block is configured to
operate in the Octet-Level Handshaking Mode.
Final Comments on Single-PHY Operation
The important thing to note about the Single-PHY
mode is that the TxUClav pin is used as a data flow
control pin, and has a role somewhat similar to RTS
(Request To Send) in RS-232 based data transmis-
sion. The TxUClav pin will have a slightly different
role when the UNI is operating in the Multi-PHY
mode.
The UNI, while operating in Single PHY mode, can be
configured for either “Octet-Level” or “Cell Level”
Handshaking. In either case, the ATM Layer processor
is expected to poll the TxUClav output pin before writ-
ing the next byte, word or cell to the TxFIFO.
F
IGURE
9. T
IMING
D
IAGRAM
OF
ATM L
AYER
PROCESSOR
T
RANSMITTING
D
ATA
TO
THE
UNI
OVER
THE
UTOPIA
D
ATA
B
US
, (S
INGLE
-PHY M
ODE
/C
ELL
-L
EVEL
H
ANDSHAKING
).
TxUClk
TxUClav
TxUEn
TxUData [15:0]
TxUSoC
W26
W0
W1
W2
W24
W22
X
X
W26
1
2
3
4
5
24
25
26
27
28
29
30
W23
W25
F
IGURE
10. T
IMING
D
IAGRAM
OF
ATM L
AYER
P
ROCESSOR
T
RANSMITTING
D
ATA
TO
THE
UNI
OVER
THE
UTOPIA
D
ATA
B
US
(S
INGLE
-PHY M
ODE
/O
CTET
-L
EVEL
H
ANDSHAKING
).
TxUClk
TxUClav
TxUEn
TxUData [15:0]
TxUSoC
W20
W21
W22
W23
W24
W25
X
X
X
W26
W0
W1
1
2
3
4
5
6
7
8
9
10
11
12