UM11029
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© NXP Semiconductors N.V. 2017. All rights reserved.
User manual
Rev. 1.0 — 16 June 2017
354 of 515
NXP Semiconductors
UM11029
Chapter 19: LPC84x I2C0/1/2/3
19.7 Functional description
19.7.1 Bus rates and timing considerations
Due to the nature of the I
2
C bus, it is generally not possible to guarantee a specific clock
rate on the SCL pin. On the I2C-bus, the The clock can be stretched by any slave device,
extended by software overhead time, etc. In a multi-master system, the master that
provides the shortest SCL high time will cause that time to appear on SCL as long as that
master is participating in I2C traffic (i.e. when it is the only master on the bus, or during
arbitration between masters).
Rate calculations give a base frequency that represents the fastest that the I
2
C bus could
operate if nothing slows it down.
19.7.1.1 Rate calculations
SCL high time (in I
2
C function clocks) = ( 1) * (MSTS 2)
SCL low time (in I
2
C function clocks) = ( 1) * (MST 2)
Nominal SCL rate = I
2
C function clock rate / (SCL high time + SCL low time)
Remark:
DIVVAL must be
≥
1.
Remark:
For 400 KHz clock rate, the clock frequency after the I
2
C divider (divval) must
be
≤
2 MHz.
shows the recommended settings for 400 KHz clock rate.
8
MONSTART
Monitor Received Start.
0
0
No detect. The monitor function has not detected a Start
event on the I
2
C bus.
1
Start detect. The monitor function has detected a Start
event on the I
2
C bus.
9
MONRESTART
Monitor Received Repeated Start.
0
0
No start detect. The monitor function has not detected a
Repeated Start event on the I
2
C bus.
1
Repeated start detect. The monitor function has
detected a Repeated Start event on the I
2
C bus.
10
MONNACK
Monitor Received NACK.
0
0
Acknowledged. The data currently being provided by the
monitor function was acknowledged by at least one
master or slave receiver.
1
Not acknowledged. The data currently being provided by
the monitor function was not acknowledged by any
receiver.
31:11 -
Reserved. Read value is undefined, only zero should be
written.
NA
Table 367. Monitor data register (MONRXDAT, address 0x4005 0080 (I2C0), 0x4005 4080
(I2C1), 0x4003 0080 (I2C2), 0x4003 4080 (I2C3)) bit description
Bit
Symbol
Value Description
Reset
value