
PRELIMINARY
XRT79L71
590
REV. P2.0.0
1-CHANNEL DS3/E3 CLEAR-CHANNEL FRAMERLIU COMBO - CC/HDLC ARCHITECTURE
The PRBS Generator and Receiver can be used in conjunction with any of the afore-mentioned "loop-back"
modes.
The LIU Analog Local Loop-back Mode
The Framer Local Loop-back Mode
Any external "Local Loop-back" Mode
7.2.1
Enabling the PRBS Pattern Generator and Receiver
The user can enable the PRBS Pattern Generator and Receiver by setting Bits 2 (RxPRBS Enable) and 3
(TxPRBS Enable), within the "Test Register" to "1" as depicted below.
Once these steps have been executed, then the PRBS Pattern Generator will be enabled and will now proceed
to fill the payload bits (within the outbound DS3 or E3 frames) with either a 2^15-1 PRBS Pattern (for DS3
Applications) or a 2^23-1 PRBS Pattern (for E3 Applications). Additionally, the PRBS Pattern Receiver will now
begin to receive the payload data-stream (from the Receive DS3/E3 Framer block) and it will begin to do all of
the following.
Check for "PRBS Lock"
Detect and Flag PRBS Bit Errors
7.2.2
Checking for "PRBS Lock"
As mentioned earlier, if the PRBS Pattern Receiver is enabled, then it will accept the payload data-stream from
the Receive DS3/E3 Framer block and it will proceed to do the following.
Check for "PRBS Lock"
Detect and Flag PRBS Bit Errors
If the PRBS Pattern Receive acquires "PRBS Lock" then it will set Bit 4 (RxPRBS Lock) within the Test
Register, to "1" as depicted below.
Test Register (Address = 0x110C)
NOTE: The user is also advise to validate the assertion of Bit 4 (RxPRBS Lock) with the state(s) of the appropriate "OOF
Defect Declared" and "LOF Defect Declared" bit-fields. In other words, for DS3 Applications, one should validate
Test Register (Address = 0x110C)
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
TxOHSrc
Unused
RxPRBS
Lock
RxPRBS
Enable
TxPRBS
Enable
Unused
R/W
R/O
R/W
R/O
0
1
0
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
TxOHSrc
Unused
RxPRBS
Lock
RxPRBS
Enable
TxPRBS
Enable
Unused
R/W
R/O
R/W
R/O
0
1
0