UM10237_2 © NXP B.V. 2008. All rights reserved.
User manual Rev. 02 — 19 December 2008 583 o f 792
NXP Semiconductors UM10237
Chapter 22: LPC24XX I2C interfaces I2C0/1/2
When STA is 1 and the I2C 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 I2C 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 I2C 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 I2C bus if it the
interface is in master mode, and transmits a START condition thereafter. If the I2C
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 I2C 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 I2C bus. When the bus detects
the STOP condition, STO is cleared automatically.
In slave mode, setting this bit can recover from an error condition. In this case, no STOP
condition is transmitted to the bus. The hardware behaves as if a STOP condition has
been received and it switches to “not addressed” slave receiver mode. The STO flag is
cleared by hardware automatically.
SI is the I2C Interrupt Flag. This bit is set when the I2C state changes. However, entering
state F8 does not set SI since there is nothing for an interrupt service routine to do in that
case.
While SI is set, the low period of the serial clock on the SCL line is stretched, and the
serial transfer is suspended. When SCL is high, it is unaffected by the state of the SI flag.
SI must be reset by software, by writing a 1 to the SIC bit in I2CONCLR register.
AA is the Assert Acknowledge Flag. When set to 1, an acknowledge (low level to SDA)
will be returned during the acknowledge clock pulse on the SCL line on the following
situations:
1. The address in the Slave Address Register has been received.
2. The general call address has been received while the general call bit (GC) in I2ADR is
set.
3. A data byte has been received while the I2C is in the master receiver mode.
4. A data byte has been received while the I2C is in the addressed slave receiver mode.
The AA bit can be cleared by writing 1 to the AAC bit in the I2CONCLR register. When AA
is 0, a not acknowledge (high level to SDA) will be returned during the acknowledge clock
pulse on the SCL line on the following situations:
1. A data byte has been received while the I2C is in the master receiver mode.
2. A data byte has been received while the I2C is in the addressed slave receiver mode.