XRT7245
DS3 UNI FOR ATM
á
PRELIMINARY
REV. 1.03
248
Bit 0—“PLOF Interrupt Status
A “1” in this bit-field indicates that the Receive PLCP
Processor has requested a “Change of PLOF” interrupt.
Note, this type of interrupt could occur due to a transi-
tion in the framing state from the “Out-of-Frame”
state to the “Un-framed” state; during which the
RxLOF pin will toggle “high”. This type of interrupt
could also occur due to a transition from the
“Un-framed” state to the “In-frame” state. It is possible
to distinguish between these two possibilities based
upon the read-in content of the Rx PLCP Configuration/
Status register. If the local μC/μP reads in a
‘xxxxx00xb” value from this register, then the “Change
in PLOF” interrupt request was due to a transition
from the “Un-framed” to the “In-frame” condition.
Conversely, if the local
μ
C/
μ
P reads in the value
“xxxxx11xb” then the “Change in PLOF” interrupt
request was due to a transition from the “Out-of-
Frame” state to the “Un-framed” state.
Bit 1—POOF Interrupt Status
A “1” in this bit-field indicates that the Receive PLCP
Processor has requested a “Change of OOF status”
interrupt. Note, this type of interrupt request could
occur due to a transition from the “Un-framed” state
to the “In-frame” state;’ during which the RxOOF pin
will toggle “l(fā)ow”. This type of interrupt could also occur
due to a transition from the “In-frame” to the “Out-of-
Frame” state. It is possible to distinguish between
these two possibilities based upon the read-in content
of the Rx PLCP Configuration/Status register. If the
local μC/μP reads in a “xxxxx0xxb” value from this
register, then the Receive PLCP Processor has tran-
sitioned from the “Un-framed” state to the “In-frame”
state. Conversely, if the local μC/μP reads in
“xxxxx1xxb”, then this indicates the transition from
the “In-frame” state to the “Out-of Frame” state.
The user can enable/disable each of these interrupts
by writing the appropriate data to the Receive PLCP
Interrupt Enable Register. This register has the exact
same bit-format as does the Receive PLCP Interrupt
Status Register. However, the bit-format of this register
is presented below for the sake of completeness.
The user can enable these interrupts by writing a “1”
to their corresponding bit-fields, in this register.
Conversely, the user can disable these interrupts by
writing a “0” to these bit fields. These bit-fields are “0”
upon power-up or reset of the UNI chip.
7.3
Receive Cell Processor
7.3.1
Brief Description of the Receive Cell
Processor
The Receive Cell Processor receives either delineated
PLCP frames from the Receive PLCP Processor, or
“Direct Mapped ATM” cells from the Receive DS3
Framer. The Receive Cell Processor will then perform
the following operations on this data.
Cell Delineation
HEC Byte Verification
Idle Cell Filtering (optional)
User/OAM Cell Filtering (optional)
Cell-payload de-scrambling (optional)
The Receive Cell Processor will also output the GFC
Nibble value of each incoming cell, via the “Receive
GFC Nibble Field” Serial Output port.
Figure 76 presents a simple block diagram of the Re-
ceive Cell Processor block along with its external pins.
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
POOF Interrupt
Enable
PLOF Interrupt
Enable
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
x
x
x
x
x
x
0
0