XRT74L73 Datasheet, PDF (447/488 Pages) Exar Corporation – 3 CHANNEL, ATM UNI/PPP DS3/E3 FRAMING CONTROLLER

PRELIMINARY
XRT74L73
3 CHANNEL, ATM UNI/PPP DS3/E3 FRAMING CONTROLLER
REV. P1.0.1
RXE3 INTERRUPT ENABLE REGISTER - 2 (ADDRESS = 0X13)
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
Not Used
TTB
Change
Interrupt
Enable
Not Used
FEBE
Interrupt
Enable
FERF
Interrupt
Enable
BIP-8
Error Interrupt
Enable
Framing
Byte Error
Interrupt
Enable
RO
R/W
RO
R/W
R/W
R/W
R/W
0
0
0
0
1
0
0
BIT 0
RxPld
Mis
Interrupt
Enable
R/W
0
• Set the Rx FERF bit-field, within the Rx E3 Configu-
ration/Status Register to “1”, as depicted below.
RXE3 CONFIGURATION & STATUS REGISTER 2 (ADDRESS = 0X11)
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
Rx LOF Algo RxLOF
RxOOF
RxLOS
RxAIS RxPld Unstab
R/W
RO
RO
RO
RO
RO
0
0
0
0
0
0
BIT 1
Rx
TMark
RO
0
BIT 0
RxFERF
RO
1
Clearing the FERF Condition
The Receive E3 Framer block will clear the FERF
condition once it has received a User-Selectable
number of E3 frames is either 3 or 5 depending upon
the value that has been written into Bit 4 (Rx FERF
Algo) of the Rx E3 Configuration/Status Register, as
discussed above.
Whenever the Receive E3 Framer clears the FERF
status, then it will do the following:
1. Generate a Change in the FERF Status Interrupt
to the Microprocessor.
2. Clear the Bit 0 (RxFERF) within the Rx E3 Con-
figuration & Status register, as depicted below.
RXE3 CONFIGURATION & STATUS REGISTER 2 (ADDRESS = 0X11)
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
Rx LOF Algo RxLOF
RxOOF
RxLOS
RxAIS
RxPld Unstab
Rx
TMark
RxFERF
R/W
RO
RO
RO
RO
RO
RO
RO
0
0
0
0
0
0
0
1
6.3.2.7 Error Checking of the Incoming E3
Frames
The Receive E3 Framer block performs error-check-
ing on the incoming E3 frame data that it receives
from the Remote Terminal Equipment. It performs
this error-checking by computing the BIP-8 value of
an incoming E3 frame. Once the Receive E3 Framer
block has obtained this value, it will compare this val-
ue with that of the “EM” byte that it receives, within
the very next E3 frame. If the locally computed BIP-8
value matches the EM byte of the corresponding E3
frame, then the Receive E3 Framer block will con-
clude that this particular frame has been properly re-
ceived. The Receive E3 Framer block will then in-
form the Remote Terminal Equipment of this fact by
having the Local Terminal Equipment Transmit E3
Framer block send the Remote Terminal an E3 frame,
with the FEBE bit-field, within the MA byte, set to “0”.
This procedure is illustrated in Figure 203 and
Figure 204 .
Figure 203 illustrates the Local Receive E3 Framer
receiving an error-free E3 frame. In this figure, the lo-
cally computed BIP-8 value of “0x5A” matches that
received from the Remote Terminal, within the EM
byte-field. Figure 204 illustrates the subsequent ac-
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