Freescale Semiconductor PowerQUICC MPC885 Reference Manual page 842

Serial Peripheral Interface (SPI)
30.6 SPI Commands
Table 30-7 lists transmit/receive commands sent to the CPM command register (CPCR).
Command
Initializes all transmit parameters in the parameter RAM to their reset state and should be issued
INIT TX
only when the transmitter is disabled. The
PARAMETERS
to reset both the Tx and Rx parameters.
Forces the SPI controller to close the current RxBD and use the next BD for subsequently received
CLOSE RXBD
data. If the controller is not receiving data, no action is taken. Use this command to extract data from
a partially full buffer.
Initializes all receive parameters in the parameter RAM to their reset state. Should be issued only
INIT RX
when the receiver is disabled. The
PARAMETERS
both the Tx and Rx parameters.
30.7 The SPI Buffer Descriptor (BD) Table
As shown in Figure 30-10, buffer descriptors (BDs) are organized into separate Rx and Tx BD tables in
dual-port RAM. The tables have the same basic configuration as the SCCs and SMCs and form circular
queues that determine the order buffers are transferred. The CPM uses BDs to confirm 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.
Dual-Port RAM
Tx Buffer
Pointer to SPI
TxBD Table
Pointer to SPI
RxBD Table
30.7.1 SPI Buffer Descriptors (BDs)
Receive and transmit BDs report information about each buffer transferred and whether a maskable
interrupt should be generated. Each 64-bit BD, shown in
structure:
• The half word at offset + 0 contains status and control bits. The CPM updates the status bits after
the buffer is sent or received.
30-12
Table 30-7. SPI Commands
INIT TX AND RX PARAMETERS
TxBD Table
Frame Status
Data Length
Buffer Pointer
RxBD Table
Frame Status
Data Length
Buffer Pointer
Figure 30-10. SPI Memory Structure
MPC885 PowerQUICC Family Reference Manual, Rev. 2
Description
command can also be used
INIT TX AND RX PARAMETERS
command can also be used to reset
External Memory
Figure 30-11 and Figure
Tx Buffer
Rx Buffer
30-12, has the following
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