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UM10316_0
© NXP B.V. 2008. All rights reserved.
User manual
Rev. 00.06 — 17 December 2008
395 of 571
NXP Semiconductors
UM10316
Chapter 23: LPC2xx I2C-interface
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 I
2
C bus
specification defines the SCL low time and high time at different values for a 400 kHz I
2
C
rate. The value of the register must ensure that the data rate is in the I
2
C data rate range
of 0 through 400 kHz. Each register value must be greater than or equal to 4.
gives some examples of I
2
C bus rates based on PCLK frequency
BASE_IVNSS_CLK and I2SCLL and I2SCLH values.
8.7 I
2
C Control Clear Register (I2C[0/1]CONCLR: 0xE008 2018,
0xE008 3018)
The I2CONCLR registers control clearing of bits in the I2CON register that controls
operation of the I
2
C interface. Writing a one to a bit of this register causes the
corresponding bit in the I
2
C control register to be cleared. Writing a zero has no effect.
AAC
is the Assert Acknowledge Clear bit. Writing a 1 to this bit clears the AA bit in the
I2CONSET register. Writing 0 has no effect.
SIC
is the I
2
C Interrupt Clear bit. Writing a 1 to this bit clears the SI bit in the I2CONSET
register. Writing 0 has no effect.
Table 329. Example I
2
C Clock Rates
I2SCLH
I
2
C Bit Frequency (kHz) at PCLK (MHz)
1
5
10
16
20
40
60
8
125
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
1.25
6.25
12.5
20
25
50
75
Table 330. I
2
C Control Set Register (I2C[0/1]CONCLR - addresses 0xE008 2018, 0xE008 3018)
bit description
Bit Symbol
Description
Reset
Value
1:0 -
Reserved. User software should not write ones to reserved bits. The
value read from a reserved bit is not defined.
NA
2
AAC
Assert acknowledge Clear bit.
3
SIC
I
2
C interrupt Clear bit.
0
4
-
Reserved. User software should not write ones to reserved bits. The
value read from a reserved bit is not defined.
NA
5
STAC
START flag Clear bit.
0
6
I2ENC
I
2
C interface Disable bit.
0
7
-
Reserved. User software should not write ones to reserved bits. The
value read from a reserved bit is not defined.
NA