32-10
MPC860 PowerQUICC UserÕs Manual
MOTOROLA
Part V. The Communications Processor Module
Figure 32-11 shows the RFCR/TFCR bit Þelds.
1
From I
2
2 base. I
2
C base = IMMR + 0x3C80.
2
Normally, these parameters need not be accessed.
0x06
MRBLR
Hword Maximum receive buffer length. DeÞnes the maximum number of bytes the I
2
C receiver
writes to a receive buffer before moving to the next buffer. The receiver writes fewer
bytes to the buffer than the MRBLR value if an error or end-of-frame occurs. Receive
buffers should not be smaller than MRBLR.
Transmit buffers are unaffected by MRBLR and can vary in length; the number of bytes
to be sent is speciÞed in TxBD[Data Length].
MRBLR is not intended to be changed while the I
2
C 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 CPM moves control to the next RxBD.
To guarantee the exact RxBD on which the change occurs, change MRBLR only while
the I
2
C 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. Reserved for CPM use.
0x0C
RPTR
Word
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 next descriptor the receiver transfers data to when it is in an
idle state or to the current descriptor during frame processing for each I
2
C channel. After
a reset or when the end of the descriptor table is reached, the CP initializes RBPTR to
the value in RBASE. Most applications should not write RBPTR, but it can be modiÞed
when the receiver is disabled or when no receive buffer is used.
0x12
RCOUNT Hword Rx internal byte count
is a down-count value that is initialized with the MRBLR value
and decremented with every byte the SDMA channels write.
0x14
RTEMP
Word
Rx temp. Reserved for CPM use.
0x18
TSTATE
Word
Tx internal state. Reserved for CPM use.
0x1C
TPTR
Word
Tx internal data pointer
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 next descriptor that the transmitter transfers data from when
it is in an idle state or to the current descriptor during frame transmission. After a reset or
when the end of the descriptor table is reached, the CPM initializes TBPTR to the value
in TBASE.Most applications should not write TBPTR, but it can be modiÞed when the
transmitter is disabled or when no transmit buffer is used.
0x22
TCOUNT Hword Tx internal byte count
is a down-count value initialized with TxBD[Data Length] and
decremented with every byte read by the SDMA channels.
0x24
TTEMP
Word
Tx temp. Reserved for CP use.
Table 32-6. I
2
C Parameter RAM Memory Map (Continued)
Offset
1
Name
Width
Description
Содержание MPC860 PowerQUICC
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