MOTOROLA
Chapter 19. Serial Communications Controllers (SCCs)
19-11
Part IV. Communications Processor Module
¥
The word at 0x4 (buffer pointer) points to the beginning of the buffer in
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.
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.
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
0
Status and Control
2
Data Length
4
High-Order Buffer Pointer
6
Low-Order Buffer Pointer
Figure 19-6. SCC Buffer Descriptors (BDs)
Summary of Contents for MPC8260 PowerQUICC II
Page 1: ...MPC8260UM D 4 1999 Rev 0 MPC8260 PowerQUICC II UserÕs Manual ª ª ...
Page 66: ...lxvi MPC8260 PowerQUICC II UserÕs Manual MOTOROLA ...
Page 88: ...1 18 MPC8260 PowerQUICC II UserÕs Manual MOTOROLA Part I Overview ...
Page 120: ...2 32 MPC8260 PowerQUICC II UserÕs Manual MOTOROLA Part I Overview ...
Page 138: ...Part II iv MPC8260 PowerQUICC II UserÕs Manual MOTOROLA Part II Configuration and Reset ...
Page 184: ...4 46 MPC8260 PowerQUICC II UserÕs Manual MOTOROLA Part II ConÞguration and Reset ...
Page 202: ...Part III vi MPC8260 PowerQUICC II UserÕs Manual MOTOROLA Part III The Hardware Interface ...
Page 266: ...8 34 MPC8260 PowerQUICC II UserÕs Manual MOTOROLA Part III The Hardware Interface ...
Page 382: ...10 106 MPC8260 PowerQUICC II UserÕs Manual MOTOROLA Part III The Hardware Interface ...
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Page 430: ...Part IV viii MOTOROLA Part IV Communications Processor Module ...
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Page 980: ...A 4 MPC8260 PowerQUICC II UserÕs Manual MOTOROLA Appendixes ...
Page 1002: ...Index 22 MPC8260 PowerQUICC II UserÕs Manual MOTOROLA INDEX ...
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