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Chapter 19. Serial Communications Controllers (SCCs)
19-11
Part IV. Communications Processor Module
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The word at offset + 0x4 (buffer pointer) points to the beginning of the buffer in
memory (internal or external).
memory (internal or external).
Ñ For an RxBD, the value must be a multiple of four. (word-aligned)
Ñ For a TxBD, this pointer can be even or odd.
Shown in Figure 19-6, the format of Tx and Rx BDs is the same in each SCC mode. Only
the status and control bits differ for each protocol.
the status and control bits differ for each protocol.
For frame-oriented protocols, a message can reside in as many buffers as necessary. Each
buffer has a maximum length of 65,535 bytes. The CPM does not assume that all buffers of
a single frame are currently linked to the BD table. The CPM does assume, however, that
the unlinked buffers are provided by the core in time to be sent or received; otherwise, an
error condition is reportedÑan underrun error when sending and a busy error when
receiving. Figure 19-7 shows the SCC BD table and buffer structure.
buffer has a maximum length of 65,535 bytes. The CPM does not assume that all buffers of
a single frame are currently linked to the BD table. The CPM does assume, however, that
the unlinked buffers are provided by the core in time to be sent or received; otherwise, an
error condition is reportedÑan underrun error when sending and a busy error when
receiving. Figure 19-7 shows the SCC BD table and buffer structure.
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
Offset + 0
Status and Control
Offset + 2
Data Length
Offset + 4
High-Order Buffer Pointer
Offset + 6
Low-Order Buffer Pointer
Figure 19-6. SCC Buffer Descriptors (BDs)