
PRELIMINARY
XRT79L71
380
REV. P2.0.0
1-CHANNEL DS3/E3 CLEAR-CHANNEL FRAMERLIU COMBO - CC/HDLC ARCHITECTURE
Generating the "Change of OOF Defect Condition" and "Change in LOF Defect Condition" Interrupts
The Receive E3 Framer block will indicate that it is generating the "Change in OOF Defect Condition" and the
"Change in LOF Defect Condition" Interrupts, by doing all of the following.
a. Asserting the Interrupt Request output pin (INT*), by pulling it "low".
b. Setting Bits 2 (Change in LOF Defect Condition Interrupt Status) and 3 (Change OOF Defect Condition
Interrupt Status) within the "Receive E3 Interrupt Status Register # 1" to "1" 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 verify that the Framing Alignment (FAS) Pattern is present at
its proper location, within the incoming E3 data-stream. In general, as long as the FAS pattern is present at its
proper location (with a small number of errors) the Receive E3 Framer block will continue to operate in the
"Frame Maintenance" Mode. However, if this Receive E3 Framer block begins to detect a large number of FAS
pattern errors within the incoming E3 data-stream, then it will exit the "In-Frame' state and will then declare the
"OOF defect condition" whenever the Receive E3 Framer block receives at least four (4) consecutive E3
frames, in which the FAS pattern was erred.
Forcing a Reframe via Software Command
The Receive DS3/E3 Framer block permits the user to command a reframe procedure with the Receive E3
Framer block via software command. The user can accomplish this by inducing a "0" to "1" transition in Bit 0
(Reframe), within the "I/O Control Register" as depicted below. Once the user executes this step, then the
Receive E3 Framer block will be forced into the Frame Acquisition Mode (or more specifically, into the "FAS
Pattern Search" State, per Figure 174) and will begin to search for the FAS pattern. The XRT79L71 will also
respond to this command by declaring both the "OOF" and "LOF Defect Conditions", and by generating the
"Change in OOF Defect Condition" and the "Change in the LOF Defect Condition" interrupts.
NOTE: After the "0" to "1" transition within Bit 0 (Reframe) has been implemented, go back and induce a "1" to "0" transition
within this bit-field.
5.3.2.3
DECLARING AND CLEARING THE LOS DEFECT CONDITION
The Receive E3 Framer block has the responsibility for declaring and clearing the LOS (Loss of Signal) defect
condition, within the incoming E3 data-stream, as described below.
Receive E3 Interrupt Status Register # 1 - G.751 (Address = 0x1114)
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
Unused
COFA
Interrupt
Status
Change in
OOF Defect
Condition
Interrupt
Status
Change in
LOF Defect
Condition
Interrupt
Status
Change in
LOS Defect
Condition
Interrupt
Status
Change in
AIS Defect
Condition
Interrupt
Status
R/O
RUR
0
1
0
I/O Control Register (Address = 0x1101)
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
Disable
TxLOC
LOC
Disable
RxLOC
Unused
Reframe
R/W
R/O
R/W
R/O
R/W
1
0
1
0
1
0
0 -> 1