XRT74L73 Datasheet, PDF (122/488 Pages) Exar Corporation – 3 CHANNEL, ATM UNI/PPP DS3/E3 FRAMING CONTROLLER

XRT74L73
3 CHANNEL, ATM UNI/PPP DS3/E3 FRAMING CONTROLLER
REV. P1.0.1
PRELIMINARY
clock rate of the TxPOHClk signal is nominally 768
kHz.
Figure 20 presents a timing diagram depicting the
behavior of the signals associated with the TxPOH
serial input interface during its use.
FIGURE 20. AN ILLUSTRATION OF THE BEHAVIOR OF THE TXPOH SERIAL INTERFACE SIGNALS DURING
USER INPUT OF POH DATA.
TxPOHClk
t18
t19
TxPOHFrame
TxPOH
t21
t20
t23
t22
TxPOHIns
The TxPOH Serial Input Port also allows the users to
externally insert their POH bytes selectively (e.g.,
some POH bytes are internally generated, others are
externally inserted). This can be accomplished by as-
serting the TxPOHIns and inserting data into the Tx-
POH input at a time when the TxPOH input is expect-
ing this data, per the byte/bit order described above.
If the remainder of the data is to be “internally” gener-
ated, the TxPOHIns pin must be negated during the
time-slot periods for those POH bytes.
2.3.3.9The “Direct Mapped ATM” Option
The UNI allows for the disabling (or by-passing) the
Transmit PLCP processor and to directly insert the
ATM cells, from the Transmit Cell Processor into the
DS3 payload. This option can be exercised by writing
to Bit 3 of the UNI Operating Mode Register, as de-
picted below.
UNI Operating Mode Register: Address = 00h
BIT 7
Local
Loopback
R/W
BIT 6
Cell
Loopback
R/W
BIT 5
PLCP
Loopback
R/W
BIT 4
Reset
R/W
BIT 3
Direct
Mapped ATM
R/W
BIT 2
C-Bit/M13
R/W
BIT 1
BIT 0
TimRefSel[1, 0]
R/W
The following table presents the relationship between
the value of this bit and the type of ATM Mapping in-
corporated.
TABLE 18: THE RELATIONSHIP BETWEEN BIT 3 OF THE UNI OPERATING MODE REGISTER AND THE RESULTING
“ATM CELL” MAPPING MODE.
BIT 3
0
1
MAPPING MODE
PLCP Mode: The PLCP is enabled. PLCP Frames will be mapped into the “outbound” DS3 Frame
Direct-Mapped ATM Mode: The PLCP Processor block is bypassed. ATM cells will be directly mapped into the
“outbound” DS3 Frame
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