MPC8280 datasheet(1071/1386 Pages) FREESCALE

1071 / 1386 page

ATM AAL1 Circuit Emulation Service

MPC8280 PowerQUICC II Family Reference Manual, Rev. 1

Freescale Semiconductor

32-11

Figure 32-8. Internal CAS Block Formats

32.4.7

Mapping VC Signaling to CAS Blocks

Each ATM channel is connected to a specific CAS block. The ATM controller implements CAS routing

tables (CRT) to maintain the routing of the signaling information from the AAL1 cells to the internal CAS

blocks for receiving, and vice versa for transmitting. Each ATM channel is connected to one receive or

transmit routing table. A CRT resides in a 32-byte space with each entry pointing to one signaling nibble.

To allow maximum flexibility with external framers, the signaling nibble can occupy the first or second

nibble in the internal CAS block (depicted in Figure 32-8).

The CRT entries should be initialized only once before the ATM channel is enabled (receiver or

transmitter). The number of entries that should be initialized must be equal to the number of active slots

(channels) in the corresponding MCC super channel. Each super channel is mapped to a unique ATM

connection (VC). The CRT entries are in ascending order based on the channel slots assigned for the MCC

super channel (depicted in Figure 32-9).

XXXX

ABCD

•

XXXX

ABCD

E1 CAS block (32 bytes)

ABCD

•

ABCD

T1 – ESF CAS block (24 bytes)

ABA’B’

•

ABA’B’

T1 – SF CAS block (24 bytes)

XXXX

ABCD

CAS block resides in the internal RAM.

To allow maximum flexibility in working

with external framers, the signaling nibble

can occupy the first or second nibble in

the CAS entry.

•

CAS block per trunk

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