XRT74L73
3 CHANNEL, ATM UNI/PPP DS3/E3 FRAMING CONTROLLER
REV. P1.0.1
PRELIMINARY
157
The bit format of the RxCP Interrupt Status Register
indicates that only three (3) bit-fields within this register
are active. The role of each of these bit fields follows.
Bit 0—HEC Byte Error Interrupt Status
A “1” in this “Reset-upon-Read” bit-field indicates the
Receive Cell Processor has detected a HEC Byte
error in an incoming cell, and has requested a “HEC
Byte Error” Interrupt, since the last read of this register.
Bit 1—“Change in LCD (Loss of Cell Delineation)
State” Interrupt Status
A “1” in this “Reset-upon-Read” bit-field indicates that
the Receive Cell Processor has changed its “LCD”
(Loss of Cell Delineation) state and has issued the
“Change in LCD State” interrupt, since the last read
of this register.
Note: This type of interrupt could occur due to a transition
from the SYNC state to the HUNT state, in the “HEC Byte
Cell Delineation Algorithm”; during which the RxLCD pin will
toggle “high”. Additionally, this type of interrupt could also
occur due to the transition from the PRE-SYNC state into
the SYNC state. The user can distinguish between these two
possibilities by reading the RxLCD bit-field (bit 7) in the RxCP
Configuration Register (Address = 4Ch).
Bit 2—Received OAM Cell Interrupt Status
A “1” in this “Reset-upon-Read” bit-field indicates that
the Receive Cell Processor has detected an OAM
Cell in the path of “incoming cells”; and has stored the
contents of this OAM cell in the “Receive OAM Cell
Buffer”, since the last read of this register. The pur-
pose of this interrupt is to alert the local μP/μC that
the “Receive OAM Cell Buffer” (within the UNI) con-
tains an OAM cell that needs to be read and
processed.
3.4Receive UTOPIA Interface Block
3.4.1Brief Description of the Receive UTOPIA
Interface Block
The Receive UTOPIA Interface Block provides a
“UTOPIA Level 2” compliant interface to interconnect
the UNI chip to ATM layer or ATM Adaptation Layer
processors, operating up to 800 Mbps. This interface
supports both an 8 and 16 bit wide data bus. Since
data is received at clock rates independent of the
ATM layer clock rate, the received cell data is written
into an internal FIFO by the Receive Cell Processor
block. This FIFO will be referred to as the RxFIFO
throughout this document. The Receive Cell Processor
will delineate, check for HEC byte errors, filter and
de-scramble ATM Cells. Whatever cells were not
discarded by the Receive Cell Processor will be
written into the RxFIFO, where it can be read out from
the UNI device by the ATM Layer Processor. The Re-
ceive UTOPIA Interface Block will inform the ATM
Layer processor that it has cell data available for
reading, by asserting the RxUClav pin “high”.
Figure 35 on the following page presents a simple il-
lustration of the Receive UTOPIA Interface block and
the associated pins.
3.4.2Functional Description of Receive UTOPIA
The purposes of the Receive UTOPIA Interface block
are to:
Receive filtered ATM cell data from the Receive
Cell Processor and make this data available to the
AAL or ATM Layer Processor.
RxCP Interrupt Status Register (Address = 4Ch)
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
Received OAM
Cell Interrupt Sta-
tus
LCD
Interrupt Status
HEC Error
Interrupt Status
RO
RO
RO
RO
RO
RUR
RUR
RUR
F
IGURE
35. S
IMPLE
B
LOCK
D
IAGRAM
OF
R
ECEIVE
UTO-
PIA B
LOCK
OF
UNI.
Receive Utopia
Interface
RxClk
RxEnB
RxPrty
RxData[15:0]
RxSoC
RxClav/RxEmptyB*
RxAddr[4:0]
From Receive Cell Processor