XRT74L73 Datasheet, PDF (89/488 Pages) Exar Corporation – 3 CHANNEL, ATM UNI/PPP DS3/E3 FRAMING CONTROLLER

PRELIMINARY
XRT74L73
3 CHANNEL, ATM UNI/PPP DS3/E3 FRAMING CONTROLLER
REV. P1.0.1
UTOPIA Configuration Register: Address = 6Ah
BIT 7
BIT 6
Unused
RO
BIT 5
Handshake Mode
R/W
BIT 4
M-PHY
R/W
BIT 3
CellOf52 Bytes
R/W
BIT 2
BIT 1
TFIFODepth[1, 0]
R/W
BIT 0
UtWidth16
R/W
The following table specifies the relationship between
this bit and the corresponding Handshaking Mode.
TABLE 5: THE RELATIONSHIP BETWEEN THE CONTENTS IN BIT FIELD 5 (HANDSHAKE MODE) WITHIN THE
UTOPIA CONFIGURATION REGISTER AND THE RESULTING UTOPIA INTERFACE HANDSHAKE MODE.
VALUE
0
1
UTOPIA INTERFACE HANDSHAKE MODE
The UTOPIA Interfaces operate in the octet level handshake mode.
The UTOPIA Interfaces operate in the cell level handshake 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.
FIGURE 6. TIMING DIAGRAM OF VARIOUS TRANSMIT UTOPIA INTERFACE BLOCK SIGNALS, WHEN THE TRANSMIT
UTOPIA INTERFACE BLOCK IS OPERATING IN THE “CELL LEVEL HANDSHAKING” MODE.
1
2
3
4
TxUClk
TxUClav
TxUEn
TxUData [15:0] _{W26 W0}
W1
W2
TxUSoC
5
24
25
26
27
28
29
30
W22 W23 W24 W25 W26 X
X
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 “low”. 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
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