2.0 Circuit Description
CX28394/28395/28398
2.2 Receiver
Quad/x16/Octal—T1/E1/J1 Framers
2.2.7 Receive Framing
Two framers are in the receive data stream: an offline framer and an online frame
status monitor. The offline framer recovers receive frame alignment; the online
framer monitors frame alignment patterns and recovers multiframe alignment in
E1 modes. Table 2-1 lists supported RCVR framing modes. Frame and
multiframe synchronization criteria used by the framers, as well as the monitoring
criteria of the online framer, are selected in RFRAME[3:0] of the Primary
Control register [CR0; addr 001]. Table 2-2 details framing loss/recovery criteria.
Receive frame synchronization is initiated by the online framer’s activation of
the Receive Loss Of Frame (RLOF) status bit in the Alarm 1 Status register
[ALM1; addr 047]. The RLOF criteria is set in the RLOFA, RLOFB, RLOFC,
and RLOFD bits of the Receiver Configuration register [RCR01; addr 040]. The
online framer supports the following LOF criteria for T1: 2 out of 4, 2 out of 5,
and 2 out of 6. For E1, the online framer supports 3 out of 3, with or without 915
out of 1000 CRC errors.
When RLOF is asserted, the offline framer automatically starts searching the
receive data stream for a new frame alignment, provided that receive framing is
enabled [RABORT; addr 040]. If receive framing is disabled, the offline framer
does not automatically search for the frame alignment, but waits for a reframe
command [RFORCE; addr 040] to start a frame alignment search. If RLOF
integration is enabled [RLOF_INTEG; addr 045] the RLOF status [ALM1; addr
047] and RLOF interrupt status [ISR7; addr 004] is integrated for 2.0 to 2.5
seconds.
The online framer continuously monitors for loss of frame (RLOF) condition
[ALM1; addr 047] and searches for E1 multiframe alignment after basic frame
alignment is recovered by the offline framer. Receive multiframe alignment is
declared when multiframe alignment criteria are met. The receive online framer
reports multiframe errors, as well as frame errors and CRC errors in the Error
Interrupt Status [ISR5; addr 006].
The offline framer is shared between the RCVR and XMTR and can search
only in one direction at any time. Consequently, the processor arbitrates which
direction is searched by enabling the reframe request (RLOF and TLOF) for that
direction.
2-10
Conexant
100054E
CONEXANT [ CONEXANT SYSTEMS, INC ]
