Datasheet
UM10398 All information provided in this document is subject to legal disclaimers. © NXP B.V. 2014. All rights reserved.
User manual Rev. 12.3 — 10 June 2014 245 of 547
NXP Semiconductors
UM10398
Chapter 15: LPC111x/LPC11Cxx I2C-bus controller
15.7.5 I
2
C SCL HIGH and LOW duty cycle registers (I2C0SCLH - 0x4000 0010
and I2C0SCLL- 0x4000 0014)
15.7.5.1 Selecting the appropriate I
2
C data rate and duty cycle
Software must set values for the registers SCLH and SCLL to select the appropriate data
rate and duty cycle. SCLH defines the number of I2C_PCLK cycles for the SCL HIGH
time, SCLL defines the number of I2C_PCLK cycles for the SCL low time. The frequency
is determined by the following formula (I2C_PCLK is the frequency of the peripheral I2C
clock):
(4)
The values for SCLL and SCLH 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. Table 226
gives
some examples of I
2
C-bus rates based on I2C_PCLK frequency and SCLL and SCLH
values.
Table 223. I
2
C Slave Address register 0 (I2C0ADR0- 0x4000 000C) bit description
Bit Symbol Description Reset value
0 GC General Call enable bit. 0
7:1 Address The I
2
C device address for slave mode. 0x00
31:8 - Reserved. The value read from a reserved bit is not defined. -
Table 224. I
2
C SCL HIGH Duty Cycle register (I2C0SCLH - address 0x4000 0010) bit
description
Bit Symbol Description Reset value
15:0 SCLH Count for SCL HIGH time period selection. 0x0004
31:16 - Reserved. The value read from a reserved bit is not defined. -
Table 225. I
2
C SCL Low duty cycle register (I2C0SCLL - 0x4000 0014) bit description
Bit Symbol Description Reset value
15:0 SCLL Count for SCL low time period selection. 0x0004
31:16 - Reserved. The value read from a reserved bit is not defined. -
Table 226. SCLL + SCLH values for selected I
2
C clock values
I
2
C mode I
2
C bit
frequency
I2C_PCLK (MHz)
6 8 10 12 16 20 30 40 50
SCLH + SCLL
Standard mode 100 kHz 60 80 100 120 160 200 300 400 500
Fast-mode 400 kHz 15 20 25 30 40 50 75 100 125
Fast-mode Plus 1 MHz - 8 10 12 16 20 30 40 50
I
2
C
bitfrequency
I2CPCLK
SCLH SCLL+
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