Serial Communications Controllers
MPC885 PowerQUICC Family Reference Manual, Rev. 2
21-12
Freescale Semiconductor
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 CP does not assume that all buffers of a single frame are currently
linked to the BD table. The CP does assume, however, that the unlinked buffers are provided by the core
in time to be sent or received; otherwise, an error condition is reported—an underrun error when sending
and a busy error when receiving.
Figure 21-7
shows the SCC BD table and buffer structure.
Figure 21-7. SCC
x
Buffer Descriptor and Buffer Structure
In all protocols, BDs can point to buffers in the internal dual-port RAM. However, because internal RAM
is used for descriptors, buffers are usually put in external RAM, especially if they are large. Usually, the
internal U bus transfers data to the buffer.
The CP processes TxBDs in a straightforward manner. Once the transmit side of an SCC is enabled, it
starts with the first BD in that SCC TxBD table. Once the CP detects that the R bit is set in the TxBD, it
starts processing the buffer. The CP detects that the BD is ready when it polls the R bit or when the user
writes to the TODR. After data from the BD is put in the Tx FIFO, if necessary the CP waits for the next
0
15
0
Status and Control
2
Data Length
4
High-Order Buffer Pointer
6
Low-Order Buffer Pointer
Figure 21-6. SCC Buffer Descriptors (BDs)
Status and Control
Data Length
Buffer Pointer
SCC RxBD Table
SCC RxBD
Table
SCC TxBD
Table
Dual-Port RAM
Status and Control
Data Length
Buffer Pointer
Tx Buffer
External Memory
Rx Buffer Descriptors
Tx Buffer Descriptors
Rx Buffer
(RBASE)
Pointer
(TBASE)
SCC TxBD Table
Pointer
Содержание PowerQUICC MPC870
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Страница 606: ...SDMA Channels and IDMA Emulation MPC885 PowerQUICC Family Reference Manual Rev 2 19 20 Freescale Semiconductor ...
Страница 738: ...SCC Asynchronous HDLC Mode and IrDA MPC885 PowerQUICC Family Reference Manual Rev 2 25 16 Freescale Semiconductor ...
Страница 780: ...SCC Ethernet Mode MPC885 PowerQUICC Family Reference Manual Rev 2 27 24 Freescale Semiconductor ...
Страница 794: ...SCC Transparent Mode MPC885 PowerQUICC Family Reference Manual Rev 2 28 14 Freescale Semiconductor ...
Страница 848: ...Serial Peripheral Interface SPI MPC885 PowerQUICC Family Reference Manual Rev 2 30 18 Freescale Semiconductor ...
Страница 882: ...Universal Serial Bus USB MPC885 PowerQUICC Family Reference Manual Rev 2 31 34 Freescale Semiconductor ...
Страница 944: ...Parallel I O Ports MPC885 PowerQUICC Family Reference Manual Rev 2 34 26 Freescale Semiconductor ...
Страница 956: ...CPM Interrupt Controller MPC885 PowerQUICC Family Reference Manual Rev 2 35 12 Freescale Semiconductor ...
Страница 1004: ...Buffer Descriptors and Connection Tables MPC885 PowerQUICC Family Reference Manual Rev 2 37 30 Freescale Semiconductor ...
Страница 1022: ...ATM Parameter RAM MPC885 PowerQUICC Family Reference Manual Rev 2 38 18 Freescale Semiconductor ...
Страница 1068: ...ATM Pace Control MPC885 PowerQUICC Family Reference Manual Rev 2 40 22 Freescale Semiconductor ...
Страница 1090: ...UTOPIA Interface MPC885 PowerQUICC Family Reference Manual Rev 2 43 8 Freescale Semiconductor ...
Страница 1120: ...AAL2 Implementation MPC885 PowerQUICC Family Reference Manual Rev 2 44 30 Freescale Semiconductor ...
Страница 1162: ...Fast Ethernet Controller FEC MPC885 PowerQUICC Family Reference Manual Rev 2 45 40 Freescale Semiconductor ...
Страница 1172: ...SEC Lite Overview MPC885 PowerQUICC Family Reference Manual Rev 2 46 8 Freescale Semiconductor ...
Страница 1176: ...SEC Lite Address Map MPC885 PowerQUICC Family Reference Manual Rev 2 47 4 Freescale Semiconductor ...
Страница 1214: ...SEC Lite Execution Units MPC885 PowerQUICC Family Reference Manual Rev 2 48 38 Freescale Semiconductor ...
Страница 1312: ...Byte Ordering MPC885 PowerQUICC Family Reference Manual Rev 2 A 8 Freescale Semiconductor ...
Страница 1313: ...MPC885 PowerQUICC Family Reference Manual Rev 2 Freescale Semiconductor B 1 Appendix B Serial Communications Performance TBD ...
Страница 1314: ...Serial Communications Performance MPC885 PowerQUICC Family Reference Manual Rev 2 B 2 Freescale Semiconductor ...
Страница 1320: ...Register Quick Reference Guide MPC885 PowerQUICC Family Reference Manual Rev 2 C 6 Freescale Semiconductor ...
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