XRT74L74 Datasheet, PDF (103/498 Pages) Exar Corporation – 4 CHANNEL, ATM UNI/PPP DS3/E3 FRAMING CONTROLLER

PRELIMINARY
XRT74L74
4 CHANNEL, ATM UNI/PPP DS3/E3 FRAMING CONTROLLER
REV. P1.1.1
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. There-
fore, a “0” must be written to this bit-field in order to
configure the UNI into the “Octet Level Handshak-
ing” mode.
Figure 6 presents a timing diagram that illustrates
the behavior of various Transmit UTOPIA Interface
block signals, when the Transmit UTOPIA Interface
block is operating 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.
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