2.0 Circuit Description
2.4 Receiver
Bt8370/8375/8376
Fully Integrated T1/E1 Framer and Line Interface
Table 2-3. Criteria for Loss/Recovery of Receive Framer Alignment (2 of 2)
Mode
SF
Description
Superframe alignment is recovered when terminal frame alignment is recovered, identifying Ft bits.
Depends on SF submode: if JYEL, only Ft bits are used; Fs bits are ignored. If no JYEL, SF pattern (001110) found
in Fs bits.
During any SF mode, loss of frame alignment (FRED) is declared when the number of frame errors detected, either
Ft or Fs bit errors, meets selected loss of frame criteria [RLOFA–RLOFC; addr 040]. FS_NFAS [addr 045]
determines whether Fs bits are included in error count.
SLC
Superframe alignment is recovered when
•
•
Terminal frame alignment is recovered, identifying Ft bits.
SLC pattern (refer to Table A-3, SLC-96 Fs Bit Contents) is found in 16 of 36 Fs bits, according to Bellcore
TR-TSY-000008.
During SLC modes without FSLOF, loss of frame alignment (FRED) is declared when the number of Ft bit errors
detected meets selected reframe criteria [RLOFA–RLOFC; addr 040].
FSLOF
ESF
FSLOF instructs the online framer to monitor 16 of 36 Fs bits (SLC multiframe pattern) for loss of frame alignment
criteria. FS_NFAS [addr 045] must also be set to include Fs bits in loss of frame. FSLOF does not affect the offline
framer's search criteria.
Extended Superframe alignment is recovered when
A valid FPS candidate is located (001011). Candidate bits are each separated by 772 digits and are received
without pattern errors.
If there is only 1 valid FPS candidate and the mode is 1 of the following:
No CRC mode—align to FPS, regardless of CRC6 comparison.
Mimic CRC mode—align to FPS, regardless of CRC6 comparison.
Force CRC mode—align to FPS, only if CRC6 is correct.
If there are two or more valid FPS candidates and the mode is 1 of the following:
No CRC mode—do not align (INVALID status).
Mimic CRC mode—align to first FPS with correct CRC6.
Force CRC mode—align to first FPS with correct CRC6.
During any ESF mode, loss of frame alignment (FRED) is declared when:
Number of FPS pattern errors detected meets selected loss of frame criteria [RLOFA–RLOFC; addr 040].
T1DM
During T1DM mode, frame alignment is recovered in two steps:
1. A 6-bit T1DM pattern (10111xx0) is found.
2. A valid F-bit pattern (Ft, Fs, or FPS) is found in the first six consecutive frames of the 12-frame cycle aligned to
the T1DM pattern.
During T1DM mode, loss of frame alignment (FRED) is declared when the number of frame errors detected, either
Ft, Fs, or T1DM errors, meets selected loss of frame criteria [RLOFA–RLOFC; addr 040].
Fs_NFAS; addr 046] does not affect T1DM mode.
NOTE(S): To meet Bellcore TA-TSY-000278, the processor must select SF + T1DM framer mode, RLOFC (2 of 6)
reframe criteria, and FS_NFAS inactive.
2-24
Conexant
N8370DSE
CONEXANT [ CONEXANT SYSTEMS, INC ]
