Motorola PowerQUICC II MPC8280 Series Reference Manual page 1123

automatic CAS mode and up to 8 blocks when in core CAS modify mode
– Support Nx64 E1/T1 channels
– CAS routing table on per-VC basis
– Automatic packing of CAS information from internal RAM to AAL1 Tx
cells
– Once per superframe, the CPM fetches the CAS information from an
external framer and updates each internal CAS block.
32.2 AAL1 CES Transmitter Overview
The MPC8280 supports both structured and unstructured AAL1 cell formats. For
unstructured format, the transmitter reads 47 bytes from the external buffer and inserts them
into the AAL1 user data field. For structured format, the transmitter reads 46 or 47 bytes
from the external buffer and inserts them into the AAL1 user data field.
32.2.1 Data Path
The AAL1 PDU header, which consists of the sequence number (SN) and the sequence
number protection (SNP) (CRC-3 and parity bit), is generated and inserted into the AAL1
Tx cell, as shown in Figure 32-1.
SN
When the transmitter operates in structured data transfer (SDT) mode, two types of AAL1
cells are defined: P (pointer) format and non-P format. The two formats are shown below.
SAR-PDU header
SAR-PDU header
The transmitter generates the structured pointer according to the I.363.1 ITU standard and
inserts the pointer exactly once every cycle (eight successive cells). The transmitter will
insert the structured pointer, at the first opportunity, into a cell with an even sequence count
(SC). When the end of the structure is not present in the current cycle, a P-format cell with
a dummy pointer (127) is inserted into the last cell (SC=6) of the cycle.
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Freescale Semiconductor, Inc.
SNP
SAR PDU header
Figure 32-1. AAL1 Transmit Cell Format
Non-P format AAL1 cell
P format AAL1 cell
ST pointer
Figure 32-2. AAL1 SDT Cell Types
Chapter 32. ATM AAL1 Circuit Emulation Service
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AAL1 CES Transmitter Overview
SAR-PDU payload
AAL1 user information
AAL1 user information
32-3