XRT74L73
3 CHANNEL, ATM UNI/PPP DS3/E3 FRAMING CONTROLLER
PRELIMINARY
REV. P1.0.1
90
The following table specifies the relationship between
this bit and the corresponding Handshaking Mode.
Note:
1. The Handshaking Mode selection applies to both the
Transmit UTOPIA Interface and Receive UTOPIA
Interface blocks.
2. Since Multi-PHY mode operation requires the use of
“Cell-Level” Handshaking, this bit-field is ignored if the
UNI is operating in the Multi-PHY mode.
3. Finally, the UNI will be operating in the “Cell-Level”
Handshaking Mode upon power up or reset. Therefore, a
“0” must be written to this bit-field in order to configure
the UNI into the “Octet Level Handshaking” mode.
Figure 6 presents a timing diagram that illustrates the
behavior of various Transmit UTOPIA Interface block sig-
nals, when the Transmit UTOPIA Interface block is operat-
ing in the “Cell-Level” Handshaking Mode.
Note: regarding Figure 6
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 6 illustrates the
ATM Layer processor writing 27 words (W0 through
W26) for each ATM cell.
In Figure 6 , the ATM Layer processor starts to write in a
new ATM cell, into the Transmit UTOPIA Interface block,
during clock edge #2. However, shortly after the ATM
Layer processor has written in word W22, TxUClav tog-
gles “l(fā)ow”. In the “Cell-Level” Handshaking mode, this
means that the ATM Layer processor is not permitted to
write in the subsequent cell (e.g., the cell which is to follow
the one that is currently being written into the Transmit
UTOPIA Interface block). Hence, the ATM Layer proces-
sor must complete writing in the current cell, and then halt
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
5: T
HE
R
ELATIONSHIP
BETWEEN
THE
CONTENTS
IN
BIT
FIELD
5 (H
ANDSHAKE
M
ODE
)
WITHIN
THE
UTOPIA C
ONFIGURATION
R
EGISTER
AND
THE
R
ESULTING
UTOPIA I
NTERFACE
H
ANDSHAKE
M
ODE
.
V
ALUE
UTOPIA I
NTERFACE
H
ANDSHAKE
M
ODE
0
The UTOPIA Interfaces operate in the octet level handshake mode.
1
The UTOPIA Interfaces operate in the cell level handshake mode.
F
IGURE
6. T
IMING
D
IAGRAM
OF
VARIOUS
T
RANSMIT
UTOPIA I
NTERFACE
BLOCK
SIGNALS
,
WHEN
THE
T
RANSMIT
UTOPIA I
NTERFACE
BLOCK
IS
OPERATING
IN
THE
“C
ELL
L
EVEL
H
ANDSHAKING
” M
ODE
.
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