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UM10375
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© NXP B.V. 2011. All rights reserved.
User manual
Rev. 3 — 14 June 2011
216 of 368
NXP Semiconductors
UM10375
Chapter 13: LPC13xx I2C-bus controller
Subsequent to an address-match detection, interrupts will be generated after each data
byte is received for a slave-write transfer, or after each byte that the module “thinks” it has
transmitted for a slave-read transfer. In this second case, the data register will actually
contain data transmitted by some other slave on the bus which was actually addressed by
the master.
Following all of these interrupts, the processor may read the data register to see what was
actually transmitted on the bus.
13.8.7.2 Loss of arbitration in Monitor mode
In monitor mode, the I
2
C module will not be able to respond to a request for information by
the bus master or issue an ACK). Some other slave on the bus will respond instead. This
will most probably result in a lost-arbitration state as far as our module is concerned.
Software should be aware of the fact that the module is in monitor mode and should not
respond to any loss of arbitration state that is detected. In addition, hardware may be
designed into the module to block some/all loss of arbitration states from occurring if those
state would either prevent a desired interrupt from occurring or cause an unwanted
interrupt to occur. Whether any such hardware will be added is still to be determined.
13.8.8 I
2
C Slave Address registers (I2C0ADR[1, 2, 3]- 0x4000 00[20, 24, 28])
These registers are readable and writable and are only used when an I
2
C interface is set
to slave mode. In master mode, this register has no effect. The LSB of I2ADR is the
General Call bit. When this bit is set, the General Call address (0x00) is recognized.
Any of these registers which contain the bit 00x will be disabled and will not match any
address on the bus. All four registers will be cleared to this disabled state on reset.
13.8.9 I
2
C Data buffer register (I2C0DATA_BUFFER - 0x4000 002C)
In monitor mode, the I
2
C module may lose the ability to stretch the clock (stall the bus) if
the ENA_SCL bit is not set. This means that the processor will have a limited amount of
time to read the contents of the data received on the bus. If the processor reads the I2DAT
shift register, as it ordinarily would, it could have only one bit-time to respond to the
interrupt before the received data is overwritten by new data.
To give the processor more time to respond, a new 8-bit, read-only DATA_BUFFER
register will be added. The contents of the 8 MSBs of the I2DAT shift register will be
transferred to the DATA_BUFFER automatically after every nine bits (8 bits of data plus
ACK or NACK) has been received on the bus. This means that the processor will have
nine bit transmission times to respond to the interrupt and read the data before it is
overwritten.
The processor will still have the ability to read I2DAT directly, as usual, and the behavior of
I2DAT will not be altered in any way.
Table 226. I
2
C Slave Address registers (I2C0ADR[1, 2, 3]- 0x4000 00[20, 24, 28]) bit
description
Bit
Symbol
Description
Reset value
0
GC
General Call enable bit.
0
7:1
Address
The I
2
C device address for slave mode.
0x00
31:8
-
Reserved. The value read from a reserved bit is not defined.
0