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UM10316_0
© NXP B.V. 2008. All rights reserved.
User manual
Rev. 00.06 — 17 December 2008
397 of 571
NXP Semiconductors
UM10316
Chapter 23: LPC2xx I2C-interface
Remark:
The ENA_SCL and MATCH_ALL bits have no effect if the MM_ENA is ‘0’ (i.e. if
the module is NOT in monitor mode).
8.8.1 Interrupt in Monitor mode
All interrupts will occur as normal when the module is in monitor mode. This means that
the first interrupt will occur when an address-match is detected (any address received if
the MATCH_ALL bit is set, otherwise an address matching one of the four address
registers).
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.
8.8.2 Loss of arbitration in Monitor mode
In monitor mode, the I2C 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.
8.9 I
2
C Data buffer register (I2DATA_BUFFER: I2C0, I2CDATA_BUFFER -
0xE008 202C; I2C1, I2C1DATA_BUFFER- 0xE008 302C)
In monitor mode, the I2C 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 msb’s 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.
Although the DATA_BUFFER register is primarily intended for use in monitor mode with
the ENA_SCL bit = ‘0’, it will be available for reading at any time under any mode of
operation.