UM10237_2 © NXP B.V. 2008. All rights reserved.
User manual Rev. 02 — 19 December 2008 586 o f 792
NXP Semiconductors UM10237
Chapter 22: LPC24XX I2C interfaces I2C0/1/2
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The values for I2SCLL and I2SCLH should not necessarily be the same. Software can set
different duty cycles on SCL by setting these two registers. For example, the I2C bus
specification defines the SCL low time and high time at different values for a 400 kHz I2C
rate. The value of the register must ensure that the data rate is in the I2C data rate range
of 0 through 400 kHz. Each register value must be greater than or equal to 4.
Table22–520 gives some examples of I2C bus rates based on PCLK frequency and
I2SCLL and I2SCLH values.
9. Details of I2C operating modes
The four operating modes are:
Master Transmitter
Master Receiver
Slave Receiver
Slave Transmitter
Data transfers in each mode of operation are shown in Figures 120 to 124. Table22–521
lists abbreviations used in these figures when describing the I2C operating modes.
Table 520. Exam ple I2C Clock Rates
I2SCLL +
I2SCLH I2C Bit Frequency (kHz) at PCLK (MHz)
1510 16 20 40 60
8125
10 100
25 40 200 400
50 20 100 200 320 400
100 10 50 100 160 200 400
160 6.25 31.25 62.5 100 125 250 375
200 5 25 50 80 100 200 300
400 2.5 12.5 25 40 50 100 150
800 1.256.2512.520 25 50 75
I2Cbitfrequency fPCLK
I2CSCLH I2CSCLL+
---------------------------------------------------------
=
Table 521. Abbre viatio ns used to describe an I2C operation
Abbreviation Explanation
S Start Condition
SLA 7 bit slave address
R Read bit (high level at SDA)
W Write bit (low level at SDA)
A Acknowledge bit (low level at SDA)