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UM10360_0
© NXP B.V. 2009. All rights reserved.
User manual
Rev. 00.06 — 5 June 2009
418 of 808
NXP Semiconductors
UM10360
Chapter 19: LPC17xx I2C0/1/2 interface
8.5 I
2
C Monitor mode control register (I2MMCTRL: I
2
C0, I2CMMCTRL0 -
0x4001 C01C; I
2
C1, I2C1MMCTRL- 0x4005 C01C; I
2
C2, I2C2MMCTRL-
0x400A 001C)
This register controls the Monitor mode which allows the I
2
C module to monitor traffic on
the I
2
C-bus without actually participating in traffic or interfering with the I
2
C-bus.
[1]
When the ENA_SCL bit is cleared and the I
2
C no longer has the ability to stretch the clock, interrupt
response time becomes important. To give the part more time to respond to an I
2
C interrupt under these
conditions, an I2DATA_BUFFER register is used (
) to hold received data for a full 9-bit word
transmission time.
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).
Table 368. I
2
C Monitor mode control register (I2MMCTRL: I
2
C0, I2CMMCTRL0 - 0x4001 C01C;
I
2
C1, I2C1MMCTRL- 0x4005 C01C; I
2
C2, I2C2MMCTRL- 0x400A 001C) bit
description
Bit Symbol
Value Description
Reset
value
0
MM_ENA
Monitor mode enable.
0
0
Monitor mode disabled.
1
The
I
2
C
module will enter monitor mode. In this mode the SDA
output will be put in high impedance mode. This prevents the
I
2
C
module from outputting data of any kind (including ACK)
onto the
I
2
C
data bus.
Depending on the state of the ENA_SCL bit, the output may
be also forced high, preventing the module from having control
over the
I
2
C
clock line.
1
ENA_SCL
SCL output enable.
0
0
When this bit is cleared to ‘0’, the SCL output will be forced
high when the module is in monitor mode. As described
above, this will prevent the module from having any control
over the
I
2
C
clock line.
1
When this bit is set, the
I
2
C
module may exercise the same
control over the clock line that it would in normal operation.
This means that, acting as a slave peripheral, the
I
2
C
module
can “stretch” the clock line (hold it low) until it has had time to
respond to an
I
2
C
interrupt.
2
MATCH_ALL
Select interrupt register match.
0
0
When this bit is cleared, an interrupt will only be generated
when a match occurs to one of the (up-to) four address
registers described above. That is, the module will respond
as a normal slave as far as address-recognition is concerned.
1
When this bit is set to ‘1’ and the
I
2
C
is in monitor mode, an
interrupt will be generated on ANY address received. This will
enable the part to monitor all traffic on the bus.