Motorola MPC860 PowerQUICC, User Manual

Page: 856 / 1106

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
2
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
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 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
2
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