
DR
AFT
DR
AFT
DRAFT
DR
D
RAFT
DRAFT
DRA
FT DRAF
D
RAFT DRAFT DRAFT DRAFT DRAFT D
DRAFT
D
RAFT DRA
FT DRAFT DRAFT DRAFT DRA
UM10360_0
© NXP B.V. 2009. All rights reserved.
User manual
Rev. 00.06 — 5 June 2009
421 of 808
NXP Semiconductors
UM10360
Chapter 19: LPC17xx I2C0/1/2 interface
8.9 I
2
C SCL HIGH duty cycle register (I2SCLH: I
2
C0, I2C0SCLH -
0x4001 C010; I
2
C1, I2C1SCLH - 0x4005 C010; I
2
C2, I2C2SCLH -
0x400A 0010)
8.10 I
2
C SCL Low duty cycle register (I2SCLL: I
2
C0 - I2C0SCLL:
0x4001 C014; I
2
C1 - I2C1SCLL: 0x4005 C014; I
2
C2 - I2C2SCLL:
0x400A 0014)
8.11 Selecting the appropriate I
2
C data rate and duty cycle
Software must set values for the registers I2SCLH and I2SCLL to select the appropriate
data rate and duty cycle. I2SCLH defines the number of PCLK_I2C cycles for the SCL
HIGH time, I2SCLL defines the number of PCLK_I2C cycles for the SCL low time. The
frequency is determined by the following formula (PCLK_I2C is the frequency of the
peripheral bus APB):
(11)
The values for I2SCLL and I2SCLH must ensure that the data rate is in the appropriate
I
2
C data rate range. Each register value must be greater than or equal to 4.
gives some examples of I
2
C-bus rates based on PCLK_I2C frequency and I2SCLL and
I2SCLH values.
Table 372. I
2
C SCL HIGH Duty Cycle register (I2SCLH: I
2
C0, I2C0SCLH - address
0x4001 C010; I
2
C1, I2C1SCLH - address 0x4005 C010; I
2
C2, I2C2SCLH -
0x400A 0010) bit description
Bit
Symbol
Description
Reset value
15:0
SCLH
Count for SCL HIGH time period selection.
0x0004
Table 373. I
2
C SCL Low duty cycle register (I2SCLL: I
2
C0 - I2C0SCLL: 0x4001 C014; I
2
C1 -
I2C1SCLL: 0x4005 C014; I
2
C2 - I2C2SCLL: 0x400A 0014) bit description
Bit
Symbol
Description
Reset value
15:0
SCLL
Count for SCL low time period selection.
0x0004
I2C
bitfrequency
PCLKI2C
I2CSCLH
I2CSCLL
+
---------------------------------------------------------
=
Table 374. Example I
2
C clock rates
I
2
C
Rate
I2SCLH values at PCLK_I2C (MHz)
6
8
10
12
16
20
30
40
50
60
70
80
90
100
100 kHz
(Standard)
60 80
100
120
160
200
300
400
500
600
700
800
900
1000
400 kHz
(Fast Mode)
15
20
25
30
40
50
75
100
125
150
175
200
225
250
1 MHz (Fast
Mode Plus)
-
8
10
12
16
20
30
40
50
60
70
80
90
100