
PRELIMINARY
XRT86SH328
297
REV. P1.0.6
28-CHANNEL DS1/E1 FRAMER/LIU WITH DS3 MUX & VT-MAPPER - SONET APPLICATIONS
N
OTE
:
For information on the criteria that the receive E1 framer block uses in order to declare the Loss of CAS Multi
Frame defect condition, please see the register description for the Framing Control Register 0xN10Bh.
BIT [3:2] - CRC Multi Frame Alignment Declaration Criteria Select[1:0]:
These bits allow the user to select which CRC Multi Frame Alignment declaration criteria the receive E1 framer block
will employ. The receive E1 framer block will check for CRC Multi Frame Alignmnet by checking the incoming E1 data
stream and determining whether the international bits (bit 1 of time slot 0) of non-FAS frames match the CRC multi frame
alignment pattern (0,0,1,0,1,1,E1,E2).
N
OTE
:
For information on the criteria that the receive E1 framer block uses to declare the Loss of CRC Multi Frame
Alignment defect condition, please see the register description for the Framing Control Register 0xN10Bh.
BIT 1 - Additional Frame Check Enable - FAS Frame Alignment Declaration:
This bit is used to configure the receive E1 framer block to perform some additional FAS frame synchronization checking
prior to declaration FAS frame alignment. If the user implements this feature, then the receive E1 framer block will
perform some more testing on two additional E1 frames, prior to declaring the FAS frame Alignment condition.
`
0 = Disabled.
`
1 = Enables additional FAS frame checking.
BIT 0 - FAS Alignment Declaration Algorithm Select:
This bit specifies which algorithm the receive E1 framer block uses in its search for the FAS alignment.
`
0 = FAS Alignment Algorithm 1
`
1 = FAS Alignment Algorithm 2
FAS Alignment Algorithm 1 Desciption
a.
Step 1: The receive E1 Framer block begins by searching for the correct 7-bit FAS pattern. Go to step 2 if
found.
b.
Step 2: Check if the FAS is absent in the following frame by verifying that bit 2 of the assumed time slot 0 of
the Non-FAS frame is a one. Go back to step 1 if failed, otherwise go to step 3.
c.
Step 3: check if the FAS is present in the assumed time slot 0 of the third frame. Go back to step 1 if failed.
After the first three steps (if all passed), the receive E1 framer block will declare FAS in Sync if Frame Check Sequence
(BIT 1 of this register) is disabled. If frame check sequence is enabled, then the receive E1 framer block will need to
verify the correct frame alignment.
FAS Alignment Algorithm 2 Description
Algorithm 2 is similar to algorithm 1 but adds a one-frame hold off time after the second step fails. After the second step
fails, it waits for the next assumed FAS in the next frame before it begins the new search for the correct FAS pattern.
CAS MF Align Sel
CAS MF A
LIGN
S
EL
[1:0]
CAS M
ULTI
F
RAME
A
LIGNMENT
D
ECLARATION
A
LGORITHM
C
RITERIA
00
CRC Multi Frame Alignment Disabled.
01
CRC Multi Frame Alignment is enabled. Alignment is declared if at least 1 valid CRC
multi frame alignment signal is observed within 8 msec.
10
CRC Multi Frame Alignment is enabled. Alignment is declared if at least 2 valid CRC
multi frame alignment signals are observed within 8 msec.
11
CRC Multi Frame Alignment is enabled. Alignment is declared if at least 3 valid CRC
multi frame alignment signals are observed within 8 msec.