XRT74L73
3 CHANNEL, ATM UNI/PPP DS3/E3 FRAMING CONTROLLER
REV. P1.0.1
PRELIMINARY
443
Finally, the Receive E3 Framer block will also inform
the external circuitry of this transition to the LOF Con-
dition state by toggling the RxLOF output pin “High”.
6.3.2.2
The Framing Maintenance Mode
Once the Receive E3 Framer block enters the In-
Frame state, then it will notify the Microprocessor/Mi-
crocontroller of this fact by generating both the
Change in OOF Condition and Change in LOF Condi-
tion Interrupts. When this happens, bits 2 and 3 (LOF
Interrupt Status and OOF Interrupt Status) will be set
to “1”, as depicted below.
Additionally, the Receive E3 Framer block will inform
the external circuitry of its transition to the In-Frame
state by toggling both the RxOOF and RxLOF output
pins "Low”.
Finally, the Receive E3 Framer block will negate both
the RxOOF and the RxLOF bit-fields within the Rx E3
Configuration & Status Register, as depicted below.
When the Receive E3 Framer block is operating in
the In-Frame state, it will then begin to perform Frame
Maintenance operations, where it will continue to ver-
ify that the Frame Alignment octets (FA1, FA2) are
present, at their proper locations. While the Receive
E3 Framer block is operating in the Frame Mainte-
nance Mode, it will declare an Out-of-Frame (OOF)
Condition if it detects invalid Framing Alignment bytes
in four consecutive frames.
Since the Receive E3 Framer block requires the de-
tection of invalid Frame Alignment bytes in four con-
secutive frames, in order for it to transition to the OOF
Condition state, it can tolerate some errors in the
Framing Alignment bytes, and still remain in the In-
Frame state. However, each time the Receive E3
Framer block detects an error in the Frame Alignment
bytes, it will increment the PMON Framing Error
Event Count Registers (Address = 0x52 and 0x53).
The bit-format for these two registers are depicted
below.
RXE3 INTERRUPT STATUS REGISTER - 1 (ADDRESS = 0X14)
B
7
B
IT
6
B
IT
5
B
IT
4
B
IT
3
B
IT
2
B
IT
1
B
IT
0
Not Used
COFA
Interrupt
Status
OOF
Interrupt
Status
LOF
Interrupt
Status
LOS
Interrupt
Status
AIS
Interrupt
Status
RO
RO
RO
RUR
RUR
RUR
RUR
RUR
0
0
0
0
0
0
0
0
RXE3 INTERRUPT STATUS REGISTER - 1 (ADDRESS = 0X14)
B
IT
7
B
IT
6
B
IT
5
B
IT
4
B
IT
3
B
IT
2
B
IT
1
B
IT
0
Not Used
COFA
Interrupt
Status
OOF
Interrupt
Status
LOF
Interrupt
Status
LOS
Interrupt
Status
AIS
Interrupt
Status
RO
RO
RO
RUR
RUR
RUR
RUR
RUR
0
0
0
0
1
1
0
0
RXE3 CONFIGURATION & STATUS REGISTER 2 (ADDRESS = 0X11)
B
IT
7
B
IT
6
B
IT
5
B
IT
4
B
IT
3
B
IT
2
B
IT
1
B
IT
0
Rx LOF Algo
RxLOF
RxOOF
RxLOS
RxAIS
RxPld Unstab
Rx
TMark
RxFERF
R/W
RO
RO
RO
RO
RO
RO
RO
0
1
1
0
0
0
0
0