NXP Semiconductors LPC1768 - Page 442

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User manual Rev. 3 — 19 December 2013 442 of 841
NXP Semiconductors
UM10360
Chapter 19: LPC176x/5x I2C0/1/2
I2EN I
2
C Interface Enable. When I2EN is 1, the I
2
C interface is enabled. I2EN can be
cleared by writing 1 to the I2ENC bit in the I2CONCLR register. When I2EN is 0, the I
2
C
interface is disabled.
When I2EN is “0”, the SDA and SCL input signals are ignored, the I
2
C block is in the “not
addressed” slave state, and the STO bit is forced to “0”.
I2EN should not be used to temporarily release the I
2
C-bus since, when I2EN is reset, the
I
2
C-bus status is lost. The AA flag should be used instead.
STA is the START flag. Setting this bit causes the I
2
C interface to enter master mode and
transmit a START condition or transmit a repeated START condition if it is already in
master mode.
When STA is 1 and the I
2
C interface is not already in master mode, it enters master mode,
checks the bus and generates a START condition if the bus is free. If the bus is not free, it
waits for a STOP condition (which will free the bus) and generates a START condition
after a delay of a half clock period of the internal clock generator. If the I
2
C interface is
already in master mode and data has been transmitted or received, it transmits a repeated
START condition. STA may be set at any time, including when the I
2
C interface is in an
addressed slave mode.
STA can be cleared by writing 1 to the STAC bit in the I2CONCLR register. When STA is
0, no START condition or repeated START condition will be generated.
If STA and STO are both set, then a STOP condition is transmitted on the I
2
C-bus if the
interface is in master mode, and transmits a START condition thereafter. If the I
2
C
interface is in slave mode, an internal STOP condition is generated, but is not transmitted
on the bus.
STO is the STOP flag. Setting this bit causes the I
2
C interface to transmit a STOP
condition in master mode, or recover from an error condition in slave mode. When STO is
1 in master mode, a STOP condition is transmitted on the I
2
C-bus. When the bus detects
the STOP condition, STO is cleared automatically.
Table 384. I
2
C Control Set register (I2CONSET: I
2
C0, I2C0CONSET - address 0x4001 C000,
I
2
C1, I2C1CONSET - address 0x4005 C000, I
2
C2, I2C2CONSET - address
0x400A 0000) bit description
Bit Symbol Description Reset
value
1:0 - Reserved. User software should not write ones to reserved bits. The
value read from a reserved bit is not defined.
NA
2 AA Assert acknowledge flag. 0
3SI I
2
C interrupt flag. 0
4 STO STOP flag. 0
5 STA START flag. 0
6I2ENI
2
C interface enable. 0
31:7 - Reserved. User software should not write ones to reserved bits. The
value read from a reserved bit is not defined.
NA