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Inter-Integrated Circuit Bus Controller Module (I
2
C)
PXN20 Microcontroller Reference Manual, Rev. 1
32-6
Freescale Semiconductor
Figure 32-5. SCL Divider and SDA Hold
Table 32-3. IBFD Field Descriptions
Field
Description
MULT
I
2
C Multiplier Factor. The MULT bits define the multiplier factor mul. This factor is used along with the SCL divider to
generate the I
2
C baud rate. The multiplier factor mul as defined by the MULT bits is provided below.
00 mul = 1
01 mul = 2
10 mul = 4
11 Reserved
ICR
I
2
C Bus Clock Rate. The ICR bits are used to prescale the bus clock for bit rate selection. These bits and the MULT
bits are used to determine the I
2
C baud rate, the SDA hold time, the SCL Start hold time and the SCL Stop hold time.
provides the SCL divider and hold values for corresponding values of the ICR.
The SCL divider multiplied by multiplier factor mul is used to generate I
2
C baud rate.
I
2
C baud rate = bus speed (Hz)/(mul * SCL divider)
Eqn. 32-1
SDA hold time is the delay from the falling edge of SDA (I
2
C data) to the changing of SDA (I
2
C data).
SDA hold time = bus period (s) * mul * SDA hold value
Eqn. 32-2
SCL Start hold time is the delay from the falling edge of SDA (I
2
C data) while SCL is high (Start condition) to the
falling edge of SCL (I
2
C clock).
SCL Start hold time = bus period (s) * mul * SCL Start hold value
Eqn. 32-3
SCL Stop hold time is the delay from the rising edge of SCL (I
2
C clock) to the rising edge of SDA
SDA (I
2
C data) while SCL is high (Stop condition).
SCL Stop hold time = bus period (s) * mul * SCL Stop hold value
Eqn. 32-4
SDA
SCL
START condition
STOP condition
SCL Hold(start)
SCL Hold(stop)
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