
XRT74L73
3 CHANNEL, ATM UNI/PPP DS3/E3 FRAMING CONTROLLER
PRELIMINARY
REV. P1.0.1
164
The UNI can be configured to operate in one of these
two handshake modes by writing the appropriate data
to Bit 5 (Handshake Mode) of the UTOPIA Configura-
tion Register, as depicted below.
The following table specifies the relationship between
this bit and the corresponding Handshaking Mode.
Note:
1. The Handshake Mode selection applies to both the
Transmit UTOPIA and Receive UTOPIA Interface
blocks.
2. Since Multi-PHY mode operation requires the use of
“Cell-Level” Handshaking; this bit 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 in order to configure
“Octet- Level Handshaking, mode.
Figure 38 presents a timing diagram that illustrates the
behavior of various Receive UTOPIA Interface block sig-
nals when the Receive UTOPIA Interface block is operat-
ing in the “Cell Level” Handshake Mode.
Note: regarding Figure 39
1. The Receive UTOPIA Data bus is configured to be
16 bits wide. Hence, the data, which the Receive
UTOPIA places on the Receive UTOPIA Data bus,
is expressed in terms of 16 bit words: W0–W26.
2. The Receive UTOPIA Interface block is configured to
handle 54 bytes/cell. Hence, Figure 39 illustrates the
ATM Layer processor reading in 27 words (W0 through
W26) for each ATM cell.
In Figure 39 , the ATM Layer processor is just finishing up
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
R/W
R/W
R/W
R/W
R/W
R/W
T
ABLE
30: T
HE
R
ELATIONSHIP
BETWEEN
THE
CONTENTS
OF
B
IT
5 (H
ANDSHAKE
M
ODE
)
WITHIN
THE
UTOPIA
C
ONFIGURATION
R
EGISTER
,
AND
THE
RESULTING
UTOPIA I
NTERFACE
H
ANDSHAKE
M
ODE
V
ALUE
R
ESULTING
H
ANDSHAKE
M
ODE
0
The UTOPIA Interfaces operate in the cell level handshake mode.
1
The UTOPIA Interfaces operate in the octet level handshake mode.
F
IGURE
38. T
IMING
D
IAGRAM
OF
VARIOUS
R
ECEIVE
UTOPIA I
NTERFACE
BLOCK
SIGNALS
,
WHEN
THE
R
ECEIVE
UTOPIA I
NTERFACE
BLOCK
IS
OPERATING
IN
THE
“C
ELL
L
EVEL
” H
ANDSHAKE
M
ODE
RxUClk
RxUClav
RxUEn
RxUData [15:0]
RxUSoC
W24
W25
W26
W0
W1
W2
W25
W26
1
2
3
4
5
6
7
8
9
31
32
34