Motorola PowerQUICC II MPC8280 Series Reference Manual page 1124

AAL1 CES Receiver Overview
The MPC8280 supports partially filled cells configured on a per-VC basis. In this mode,
only the valid octets are filled with user information; the rest of the cell is filled with
padding octets.
The MPC8280 supports synchronous residual time stamp (SRTS) generation using an
external PLL. If this mode is enabled, the MPC8280 reads the SRTS code from external
logic and inserts it into four outgoing cells. See Section 31.16, "SRTS Generation and
Clock Recovery Using External Logic."
32.2.2 Signaling Path
The MPC8280 automatically handles the signaling information as part of the interworking
function. The ATM transmitter packs the signaling information at the end of each
superframe during the data segmentation process. Each VC is associated to one signaling
block by an internal routing table; see Section 32.4.6, "Channel Associated Signaling
(CAS) Support." The signaling information that resides in the internal RAM is inserted into
the AAL1 cell according to the af-vtoa-0078 specification.
The AAL1 structure is divided into two sections. The first section carries the Nx64 payload,
and the second carries the signaling bits that are associated with the payload.
The MPC8280 supports two framing modes: one for Nx64 DS1 ESF (extended superframe)
framing, and the other for Nx64 E1 G.704 framing. See Figure 32-3. Each of the internal
signaling blocks can be used to deliver only one of the framing formats; that is, they cannot
be changed dynamically.
ABCD
AAL1 block T1 framing
Note: The CAS block size is (N+1) nibble if N is an odd number.
32.3 AAL1 CES Receiver Overview
The ATM controller supports both AAL1 structured and unstructured formats. For the
unstructured format, 47 octets are copied to the current receive buffer and for the structured
format, 46 (P format) or 47 (non-P format) octets are copied to the current receive buffer.
32-4
Freescale Semiconductor, Inc.
24xNx64
•
•
•
N signaling
nibbles
ABCD
Figure 32-3. AAL1 Framing Formats
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16xNx64
•
•
•
ABCD
N signaling
nibbles
ABCD
AAL1 block E1 framing
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