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MCF51QE128 MCU Series Reference Manual, Rev. 3
Freescale Semiconductor 2-269
13.3.5 IIC Data I/O Register (IICD)
NOTE
When transitioning out of master receive mode, the IIC mode should be
switched before reading the IICD register to prevent an inadvertent
initiation of a master receive data transfer.
In slave mode, the same functions are available after an address match has occurred.
The TX bit in IICC must correctly reflect the desired direction of transfer in master and slave modes for
the transmission to begin. For instance, if the IIC is configured for master transmit but a master receive is
desired, reading the IICD does not initiate the receive.
Reading the IICD returns the last byte received while the IIC is configured in master receive or slave
receive modes. The IICD does not reflect every byte transmitted on the IIC bus, nor can software verify
that a byte has been written to the IICD correctly by reading it back.
In master transmit mode, the first byte of data written to IICD following assertion of MST is used for the
address transfer and should comprise of the calling address (in bit 7 to bit 1) concatenated with the required
R/W bit (in position bit 0).
13.3.6 IIC Control Register 2 (IICC2)
76543210
R
DATA
W
Reset00000000
Figure 13-7. IIC Data I/O Register (IICD)
Table 13-8. IICD Field Descriptions
Field Description
7–0
DATA
Data — In master transmit mode, when data is written to the IICD, a data transfer is initiated. The most significant
bit is sent first. In master receive mode, reading this register initiates receiving of the next byte of data.
76543210
R
GCAEN ADEXT
000
AD10 AD9 AD8
W
Reset00000000
= Unimplemented or Reserved
Figure 13-8. IIC Control Register (IICC2)