UM10462
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User manual
Rev. 5.5 — 21 December 2016
304 of 523
NXP Semiconductors
UM10462
Chapter 14: LPC11U3x/2x/1x I2C-bus controller
via the I
2
C Clock Control Registers. See the description of the I2CSCLL and I2CSCLH
registers for details. The output clock pulses have a duty cycle as programmed unless the
bus is synchronizing with other SCL clock sources as described above.
14.8.8 Timing and control
The timing and control logic generates the timing and control signals for serial byte
handling. This logic block provides the shift pulses for DAT, enables the comparator,
generates and detects START and STOP conditions, receives and transmits acknowledge
bits, controls the master and slave modes, contains interrupt request logic, and monitors
the I
2
C-bus status.
14.8.9 Control register, CONSET and CONCLR
The I
2
C control register contains bits used to control the following I
2
C block functions: start
and restart of a serial transfer, termination of a serial transfer, bit rate, address recognition,
and acknowledgment.
The contents of the I
2
C control register may be read as CONSET. Writing to CONSET will
set bits in the I
2
C control register that correspond to ones in the value written. Conversely,
writing to CONCLR will clear bits in the I
2
C control register that correspond to ones in the
value written.
14.8.10 Status decoder and status register
The status decoder takes all of the internal status bits and compresses them into a 5-bit
code. This code is unique for each I
2
C-bus status. The 5-bit code may be used to
generate vector addresses for fast processing of the various service routines. Each
service routine processes a particular bus status. There are 26 possible bus states if all
four modes of the I
2
C block are used. The 5-bit status code is latched into the five most
significant bits of the status register when the serial interrupt flag is set (by hardware) and
remains stable until the interrupt flag is cleared by software. The three least significant bits
of the status register are always zero. If the status code is used as a vector to service
routines, then the routines are displaced by eight address locations. Eight bytes of code is
sufficient for most of the service routines (see the software example in this section).
14.9 I
2
C operating modes
In a given application, the I
2
C block may operate as a master, a slave, or both. In the slave
mode, the I
2
C hardware looks for any one of its four slave addresses and the General Call
address. If one of these addresses is detected, an interrupt is requested. If the processor
wishes to become the bus master, the hardware waits until the bus is free before the
master mode is entered so that a possible slave operation is not interrupted. If bus
arbitration is lost in the master mode, the I
2
C block switches to the slave mode
immediately and can detect its own slave address in the same serial transfer.
14.9.1 Master Transmitter mode
In this mode data is transmitted from master to slave. Before the master transmitter mode
can be entered, the CONSET register must be initialized as shown in
must be set to 1 to enable the I
2
C function. If the AA bit is 0, the I
2
C interface will not
acknowledge any address when another device is master of the bus, so it can not enter
