Motorola PowerQUICC II MPC8280 Series Reference Manual page 1377

After 5 bytes are sent, the TxBD is closed. Additionally, the Rx buffer is closed after 5 bytes
are received because TxBD[L] is set.
39.9 SPI Slave Programming Example
The following is an example initialization sequence to follow when the SPI is in slave
mode. It is very similar to the SPI master example, except that SPISEL is used instead of a
general-purpose I/O signal (as shown in Figure 39-2).
1. Enable SPIMISO, SPIMOSI, SPICLK, and SPISEL.
2. In address 0x89FC, assign a pointer to the SPI parameter RAM.
3. Assuming one RxBD at the beginning of the dual-port RAM followed by one
TxBD, write RBASE with 0x0000 and TBASE with 0x0008 in the SPI parameter
RAM.
4. Write RFCR and TFCR with 0x10 for normal operation.
5. Program MRBLR = 0x0010 for 16 bytes, the maximum number of bytes per buffer.
6. Initialize the RxBD. Assume the Rx buffer is at 0x0000_1000 in main memory.
Write 0xB000 to RxBD[Status and Control], 0x0000 to RxBD[Data Length]
(optional), and 0x0000_1000 to RxBD[Buffer Pointer].
7. Initialize the TxBD. Assume the Tx buffer is at 0x0000_2000 in main memory and
contains five 8-bit characters. Write 0xB800 to TxBD[Status and Control], 0x0005
to TxBD[Data Length], and 0x0000_2000 to TxBD[Buffer Pointer].
8. Execute the
INIT RX AND TX PARAMETERS
CPCR.
9. Write 0xFF to SPIE to clear any previous events.
10. Write 0x37 to SPIM to enable all SPI interrupts.
11. Set SPMODE to 0x0170 to enable normal operation (not loopback), slave mode,
SPI enabled, and 8-bit characters. BRG speed is ignored in slave mode.
12. Set SPCOM[STR] to enable the SPI to be ready once the master begins the transfer.
If the master sends 3 bytes and negates SPISEL, the RxBD is
closed but the TxBD remains open. If the master sends 5 or
more bytes, the TxBD is closed after the fifth byte. If the master
sends 16 bytes and negates SPISEL, the RxBD is closed
without triggering an out-of-buffers error. If the master sends
more than 16 bytes, the RxBD is closed (full) and an
out-of-buffers error occurs after the 17th byte is received.
MOTOROLA
Freescale Semiconductor, Inc.
NOTE
Chapter 39. Serial Peripheral Interface (SPI)
For More Information On This Product,
Go to: www.freescale.com
SPI Slave Programming Example
command by writing 0x2541_0000 to
39-19