I
2
C Controller
MPC885 PowerQUICC Family Reference Manual, Rev. 2
Freescale Semiconductor
32-13
32.7.1.2
I
2
C Transmit Buffer Descriptor (TxBD)
Transmit data is arranged in buffers referenced by TxBDs in the TxBD table. The first word of the TxBD,
shown in
Figure 32-14
, contains status and control bits.
Table 32-10
describes I
2
C TxBD status and control bits.
2
W
Wrap (last BD in table).
0 Not the last BD in the RxBD table.
1 Last BD in the RxBD table. After this buffer is used, the CPM receives incoming data using the
BD pointed to by RBASE (top of the table). The number of BDs in this table is determined only by
the W bit.
3
I
Interrupt.
0 No interrupt is generated after this buffer is full.
1 The I2CER[RXB] is set when the CPM fills this buffer, indicating that the core needs to process
the buffer. The RXB bit can cause an interrupt if it is enabled.
4
L
Last. The I
2
C controller sets L.
0 This buffer does not contain the last character of the message.
1 This buffer holds the last character of the message. The I
2
C controller sets L after all received
data is placed into the associated buffer, or because of a stop or start condition or an overrun.
5–13
—
Reserved and should be cleared.
14
OV
Overrun. Set when a receiver overrun occurs during reception. The I
2
C controller updates this bit
after the received data is placed into the associated buffer.
15
—
Reserved and should be cleared.
0
1
2
3
4
5
6
12
13
14
15
0
R
—
W
I
L
S
—
NAK
UN
CL
2
Data Length
4
Tx Buffer Pointer
6
Figure 32-14. I
2
C Transmit Buffer Descriptor (TxBD)
Table 32-10. I
2
C TxBD Status and Control Bits
Bits
Name
Description
0
R
Ready
0 The buffer is not ready to be sent. This BD or its buffer can be modified. The CPM clears R after
the buffer is sent or an error occurs.
1 The buffer is ready for transmission or is being sent. The BD cannot be modified once R is set.
1
—
Reserved and should be cleared.
2
W
Wrap (last BD in TxBD table)
0 Not the last BD in the table
1 Last BD in the table. After this buffer is used, the CPM transmits data using the BD pointed to by
TBASE (top of the table). The number of BDs in this table is determined only by the W bit.
Table 32-9. I
2
C RxBD Status and Control Bits (continued)
Bits
Name
Description
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