
MOTOROLA
Chapter 30. Serial Management Controllers
30-5
Part V. The Communications Processor Module
30.2.2 SMC Buffer Descriptors (BDs)
In UART and transparent modes, the SMCÕs memory structure is like the SCCÕs in that
SMC-associated data is stored in buffers. Each buffer is referenced by a BD and organized
in a BD table located in the dual-port RAM. See Figure 30-3.
Figure 30-3. SMC Memory Structure
The BD table allows buffers to be deÞned for transmission and reception. Each table forms
a circular queue. The CP uses BDs to conÞrm reception and transmission so that the
processor knows buffers have been serviced. The data resides in external or internal buffers.
When SMCs are conÞgured to operate in GCI mode, their memory structure is predeÞned
to be one half-word long for transmit and one half-word long for receive. For more
information on these half-word structures, see Section 30.5, ÒSMC in GCI Mode.Ó
30.2.3 SMC Parameter RAM
Each SMC parameter RAM area begins at the same offset from each SMC base. The
protocol-speciÞc portions of the SMC parameter RAM are discussed in the sections that
follow. The SMC parameter RAM shared by the UART and transparent protocols is shown
in Table 30-2. Parameter RAM for GCI protocol is described in Section 30.5.1, ÒSMC GCI
Parameter RAM.Ó
Status and Control
Data Length
Buffer Pointer
Pointer to SMCx
TxBD Table
Pointer to SMCx
RxBD Table
SMC RxBD
Table
SMC TxBD
Table
Dual-Port RAM
Status and Control
Data Length
Buffer Pointer
Tx Data Buffer
External Memory
RxBD Table
TxBD Table
Rx Data Buffer
Содержание MPC860 PowerQUICC
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