Motorola MPC8260 - Manual (Page 935)

MOTOROLA Chapter 33. Serial Peripheral Interface (SPI) 33-11
Part IV. Communications Processor Module
0x06 MRBLR Hword Maximum receive buffer length. The SPI has one MRBLR entry to deÞne the maximum
number of bytes the MPC8260 writes to a Rx buffer before moving to the next buffer. The
MPC8260 can write fewer bytes than MRBLR if an error or end-of-frame occurs, but
never exceeds the MRBLR value. User-supplied buffers should be no smaller than
MRBLR.
Tx buffers are unaffected by MRBLR and can have varying lengths; the number of bytes
to be sent is programmed in TxBD[Data Length].
MRBLR is not intended to be changed while the SPI is operating. However it can be
changed in a single bus cycle with one 16-bit move (not two 8-bit bus cycles back-to-
back). The change takes effect when the CP moves control to the next RxBD. To
guarantee the exact RxBD on which the change occurs, change MRBLR only while the
SPI receiver is disabled. MRBLR should be greater than zero; it should be an even
number if the character length of the data exceeds 8 bits.
0x08 RSTATE Word Rx internal state. 2 Reserved for CP use.
0x0C Ñ Word The Rx internal data pointer 2 is updated by the SDMA channels to show the next
address in the buffer to be accessed.
0x10 RBPTR Hword RxBD pointer. Points to the current Rx BD being processed or to the next BD to be
serviced when idle. After a reset or when the end of the BD table is reached, the CP
initializes RBPTR to the RBASE value. Most applications should not modify RBPTR, but
it can be updated when the receiver is disabled or when no Rx buffer is in use.
0x12 Ñ Hword The Rx internal byte count 2 is a down-count value that is initialized with the MRBLR
value and decremented with every byte the SDMA channels write.
0x14 Ñ Word Rx temp. 2 Reserved for CP use.
0x18 TSTATE Word Tx internal state. 2 Reserved for CP use.
0x1C Ñ Word The Tx internal data pointer 2 is updated by the SDMA channels to show the next address
in the buffer to be accessed.
0x20 TBPTR Hword TxBD pointer. Points to the current Tx BD during frame transmission or the next BD to be
processed when idle. After reset or when the end of the Tx BD table is reached, the CP
initializes TBPTR to the TBASE value. Most applications do not need to modify TBPTR,
but it can be updated when the transmitter is disabled or when no Tx buffer is in use.
0x22 Ñ Hword The Tx internal byte count 2 is a down-count value initialized with TxBD[Data Length] and
decremented with every byte read by the SDMA channels.
0x24 Ñ Word Tx temp. 2 Reserved for CP use.
0x34 Ñ Word SDMA temp.
1 From the pointer value programmed in SPI_BASE at IMMR + 0x89FC.
2 Normally, these parameters need not be accessed. They are listed to help experienced users in debugging.
Table 33-5. SPI Parameter RAM Memory Map (Continued)
Offset 1 Name Width Description