XRT72L56
SIX CHANNEL DS3/E3 FRAMER IC WITH HDLC CONTROLLER
á
PRELIMINARY
REV. P1.1.2
209
clare itself in the In-Frame condition, and will begin
Frame Maintenance operations. The Receive DS3
Framer block will then indicate that it has transitioned
from the OOF condition into the In-Frame condition by
doing the following.
Generate a Change in OOF Condition interrupt to
the local μP
Negate the RxOOF output pin (e.g., toggle it
"Low").
RX DS3 CONFIGURATION AND STATUS REGISTER, (ADDRESS = 0X10)
Negate the RxOOF bit-field (Bit 4) within the
Receive DS3 Configuration and Status Register.
The user can configure the Receive DS3 Framer to
operate such that 'valid parity' (P-bits) must also be
detected before the Receive DS3 Framer can declare
itself In Frame. The user can set this configuration by
writing the appropriate data to the Rx DS3 Configura-
tion and Status Register, as depicted below.
Table 38 relates the contents of this bit field to the
framing acquisition criteria.
Once the Receive DS3 Framer block is operating in
the In-Frame condition, normal data recovery and
processing of the DS3 data stream begins. The max-
imum average reframing time is less than 1.5 ms.
4.3.2.2
Frame Maintenance Mode Operation
When the Receive DS3 Framer block is operating in
the In-Frame state (per Figure 81), it will then begin to
perform Frame Maintenance operations, where it will
continue to verify that the F- and M-bits are present,
at their proper locations. While the Receive DS3
Framer block is operating in the Frame Maintenance
mode, it will declare an Out-of-Frame (OOF) condition
if 3 or 6 F-bits (depending upon user selection) out of
16 consecutive F-bits are in error. The user makes
this selection for the OOF Declaration criteria by writ-
ing the appropriate value to bit 1 (F-Sync Algo) of the
Rx DS3 Configuration and Status Register, as depict-
ed below.
Table 39 relates the contents of this bit-field to the
OOF Declaration criteria
B
IT
7
B
IT
6
B
IT
5
B
IT
4
B
IT
3
B
IT
2
B
IT
1
B
IT
0
RxAIS
RxLOS
RxIdle
RxOOF
Int LOS
Disable
R/W
X
Framing on
Parity
R/W
X
F-Sync Algo
M-Sync Algo
RO
X
RO
X
RO
X
RO
X
R/W
X
R/W
X
T
ABLE
38: T
HE
R
ELATIONSHIP
BETWEEN
THE
CONTENTS
OF
B
IT
2 (F
RAMING
ON
P
ARITY
)
WITHIN
THE
R
X
DS3
C
ONFIGURATION
AND
S
TATUS
R
EGISTER
,
AND
THE
RESULTING
F
RAMING
A
CQUISITION
C
RITERIA
F
RAMING
ON
P
ARITY
(B
IT
2)
F
RAMING
A
CQUISITION
C
RITERIA
0
The In-frame is declared after F-bit synchronization (10 F-bit matches) followed by M-bit synchronization (M-
bit matches for 3 DS3 M-frames)
1
The In-frame condition is declared after F-bit synchronization, followed by M-bit synchronization, with valid
parity over the frames. Also, the occurrence of parity errors in 2 or more out of 5 frames starts a frame search
RX DS3 CONFIGURATION AND STATUS REGISTER, (ADDRESS = 0X10)
B
IT
7
B
IT
6
B
IT
5
B
IT
4
B
IT
3
B
IT
2
B
IT
1
B
IT
0
RxAIS
RxLOS
RxIdle
RxOOF
Int LOS
Disable
R/W
X
Framing on
Parity
R/W
X
F-Sync Algo
M-Sync Algo
RO
X
RO
X
RO
X
RO
X
R/W
X
R/W
X