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I
2
C Interface
33-5
Freescale Semiconductor
33.2.4
I
2
C Status Register (I2SR)
I2SR contains bits that indicate transaction direction and status.
Table 33-4. I2CR Field Descriptions
Field
Description
7
IEN
I
2
C enable. Controls the software reset of the entire I
2
C module. If the module is enabled in the middle of a byte
transfer, slave mode ignores the current bus transfer and starts operating when the next START condition is detected.
Master mode is not aware that the bus is busy; initiating a start cycle may corrupt the current bus cycle, ultimately
causing the current master or the I
2
C module to lose arbitration, after which bus operation returns to normal.
0 The I
2
C module is disabled, but registers can be accessed.
1 The I
2
C module is enabled. This bit must be set before any other I2CR bits have any effect.
6
IIEN
I
2
C interrupt enable.
0 I
2
C module interrupts are disabled, but currently pending interrupt condition is not cleared.
1 I
2
C module interrupts are enabled. An I
2
C interrupt occurs if I2SR[IIF] is also set.
5
MSTA
Master/slave mode select bit. If the master loses arbitration, MSTA is cleared without generating a STOP signal.
0 Slave mode. Changing MSTA from 1 to 0 generates a STOP and selects slave mode.
1 Master mode. Changing MSTA from 0 to 1 signals a START on the bus and selects master mode.
4
MTX
Transmit/receive mode select bit. Selects the direction of master and slave transfers.
0 Receive
1 Transmit. When the device is addressed as a slave, software must set MTX according to I2SR[SRW]. In master
mode, MTX must be set according to the type of transfer required. Therefore, when the MCU addresses a slave
device, MTX is always 1.
3
TXAK
Transmit acknowledge enable. Specifies the value driven onto I2C_SDA during acknowledge cycles for master and
slave receivers. Writing TXAK applies only when the I
2
C bus is a receiver.
0 An acknowledge signal is sent to the bus at the ninth clock bit after receiving one byte of data.
1 No acknowledge signal response is sent (acknowledge bit = 1).
2
RSTA
Repeat start. Always read as 0. Attempting a repeat start without bus mastership causes loss of arbitration.
0 No repeat start
1 Generates a repeated START condition.
1–0
Reserved, must be cleared.
Address: 0xFC05_800C (I2SR)
Access: User read/write
7
6
5
4
3
2
1
0
R
ICF
IAAS
IBB
IAL
0
SRW
IIF
RXAK
W
Reset:
1
0
0
0
0
0
0
1
Figure 33-5. I
2
C Status Register (I2SR)
Summary of Contents for MCF54455
Page 33: ...xxviii Freescale Semiconductor ...
Page 67: ...Freescale Semiconductor 1 ...
Page 125: ...Freescale Semiconductor 1 ...
Page 145: ...Enhanced Multiply Accumulate Unit EMAC 5 21 Freescale Semiconductor ...
Page 173: ...Cache 6 28 Freescale Semiconductor ...
Page 179: ...Static RAM SRAM 7 6 Freescale Semiconductor ...
Page 207: ...Power Management 9 16 Freescale Semiconductor ...
Page 323: ...Reset Controller Module 13 8 Freescale Semiconductor ...
Page 389: ...Pin Multiplexing and Control 16 44 Freescale Semiconductor ...
Page 575: ...PCI Bus Controller 22 58 Freescale Semiconductor ...
Page 600: ...Advanced Technology Attachment ATA Freescale Semiconductor 23 25 ...
Page 601: ...Freescale Semiconductor 1 ...
Page 842: ...I2 C Interface Freescale Semiconductor 33 16 ...
Page 843: ...Freescale Semiconductor 1 ...
Page 921: ...Revision History A 6 Freescale Semiconductor ...