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UM10316_0
© NXP B.V. 2008. All rights reserved.
User manual
Rev. 00.06 — 17 December 2008
393 of 571
NXP Semiconductors
UM10316
Chapter 23: LPC2xx I2C-interface
SI
is the I
2
C Interrupt Flag. This bit is set when the I
2
C 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 I
2
C is in the master receiver mode.
4. A data byte has been received while the I
2
C 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 I
2
C is in the master receiver mode.
2. A data byte has been received while the I
2
C is in the addressed slave receiver mode.
8.2 I
2
C Status Register (I2C[0/1]STAT - 0xE008 2004, 0xE008 3004)
Each I
2
C Status register reflects the condition of the corresponding I
2
C interface. The I
2
C
Status register is Read-Only.
The three least significant bits are always 0. Taken as a byte, the status register contents
represent a status code. There are 26 possible status codes. When the status code is
0xF8, there is no relevant information available and the SI bit is not set. All other 25 status
codes correspond to defined I
2
C states. When any of these states entered, the SI bit will
be set. For a complete list of status codes, refer to tables from
to
8.3 I
2
C Data Register (I2C[0/1]DAT - 0xE008 2008, 0xE008 3008)
This register contains the data to be transmitted or the data just received. The CPU can
read and write to this register only while it is not in the process of shifting a byte, when the
SI bit is set. Data in I2DAT remains stable as long as the SI bit is set. Data in I2DAT is
always shifted from right to left: the first bit to be transmitted is the MSB (bit 7), and after a
byte has been received, the first bit of received data is located at the MSB of I2DAT.
Table 324. I
2
C Status Register (I2C[0/1]STAT - addresses 0xE008 2004, 0xE008 3004) bit
description
Bit Symbol
Description
Reset Value
2:0 -
These bits are unused and are always 0.
0
7:3 Status
These bits give the actual status information about the I
2
C interface. 0x1F