Motorola PowerQUICC II MPC8280 Series Reference Manual page 1132

Interworking Functions
information unpacked from the AAL1 cells (ATM-to-TDM), and the other contains the
signaling information fetched from an external framer (TDM-to-ATM). All 8 CAS blocks
reside in the internal RAM.
E1 CAS block (32 bytes)
0 XXXX
1 XXXX
• XXXX
•
•
•
•
31 XXXX
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.
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).
32-12
Freescale Semiconductor, Inc.
CAS block per trunk
ABCD
ABCD
ABCD
•
•
ABCD
T1 – SF CAS block (24 bytes)
0 XXXX
1 XXXX
• XXXX
•
•
•
•
23 XXXX
MPC8280 PowerQUICC II Family Reference Manual
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T1 – ESF CAS block (24 bytes)
0 XXXX ABCD
1 XXXX ABCD
• XXXX ABCD
•
• •
•
• •
23 XXXX ABCD
ABA'B'
ABA'B'
1
ABA'B'
•
ABCD
•
ABA'B'
ABCD XXXX
2
ABCD
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