
Programming Model
MOTOROLA
I2C Modules
18-11
18.5.5
I2C DATA I/O REGISTERS (MBDR)
When an address and R/W bit is written to the MBDR and the I2C is the master, a transmission will start.
When data is written to the MBDR, a data transfer is initiated. The most significant bit is sent first in both
cases. In the master-receive mode, reading the MBDR register allows the read to occur but also initiates
next byte data receiving. In slave mode, the same function is available after it is addressed.
SRW
When IAAS is set, the Slave Read/Write bit indicates the value of the R/W command bit of
the calling address sent from the master. This bit is valid only when:
A complete transfer has occurred and no other transfers have been initiated.
I2C is a slave and has an address match.
Checking this bit, the CPU can select slave transmit/receive mode according to the
command of the master.
1 = Slave transmit, master reading from slave
0 = Slave receive, master writing to slave
IIF
The I2C Interrupt (IIF) bit is set when an interrupt is pending, which will cause a processor
interrupt request (provided IIEN is set). IIF is set when one of the following events occurs:
Complete one byte transfer (set at the falling edge of the 9th clock)
Receive a calling address that matches its own specific address in slave-receive mode
Arbitration lost
This bit must be cleared by software by writing a zero to it in the interrupt routine.
RXAK
The value of SDA during the acknowledge bit of a bus cycle. If the received acknowledge bit
(RXAK) is low, it indicates an acknowledge signal has been received after the completion of
8 bits data transmission on the bus. If RXAK is high, it means no acknowledge signal has
been detected at the 9th clock.
1 = No acknowledge received
0 = Acknowledge received
Table 18-11 MBDR Register
BITS
7
6
5
4
3
2
1
0
FIELD
D7D6
D5D4
D3D2
D1D0
RESET
000
00
0
R/W
READ/WRITE SUPERVISOR OR USER MODE
ADDR
MBAR+$290 (MBDR)
MBAR2+$450 (MBDR2)
Table 18-10 MBSR Bit Descriptions (Continued)
BIT NAME
DESCRIPTION
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Freescale Semiconductor, Inc.
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