MOTOROLA
Chapter 31. Serial Peripheral Interface
31-13
Part V. The Communications Processor Module
31.6 SPI Commands
Table 31-7 lists transmit/receive commands sent to the CPM command register (CPCR).
31.7 The SPI Buffer Descriptor (BD) Table
As shown in Figure 31-10, buffer descriptors (BDs) are organized into separate Rx and Tx
BD tables in dual-port RAM. The tables have the same basic conÞguration as for the SCCs
and SMCs and form circular queues that determine the order buffers are transferred. The
CPM uses BDs to conÞrm reception and transmission or to indicate error conditions so that
the core knows buffers have been serviced. The buffers themselves can be placed in external
memory or in any unused parameter area of the dual-port RAM.
Figure 31-10. SPI Memory Structure
Table 31-7. SPI Commands
Command
Description
INIT
TX
PARAMETERS
Initializes all transmit parameters in the parameter RAM to their reset state and should be issued only
when the transmitter is disabled. The
INIT
TX
AND
RX
PARAMETERS
command can also be used to reset
both the Tx and Rx parameters.
CLOSE
RXBD
Forces the SPI controller to close the current RxBD and use the next BD for subsequently received data.
If the controller is not receiving data, no action is taken. Use this command to extract data from a
partially full buffer.
INIT
RX
PARAMETERS
Initializes all receive parameters in the parameter RAM to their reset state. Should be issued only when
the receiver is disabled. The
INIT
TX
AND
RX
PARAMETERS
command can also be used to reset both the Tx
and Rx parameters.
Frame Status
Data Length
Buffer Pointer
Frame Status
Data Length
Buffer Pointer
Tx Buffer
Pointer to SPI
RxBD Table
Rx Buffer
Dual-Port RAM
External Memory
TxBD Table
RxBD Table
Tx Buffer
Pointer to SPI
TxBD Table
Summary of Contents for MPC860 PowerQUICC
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Page 325: ...MOTOROLA Part IV Hardware Interface IV v Part IV Hardware Interface ...
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