MC9S08SG8 Datasheet, PDF (164/310 Pages) Freescale Semiconductor, Inc – Microcontrollers

Inter-Integrated Circuit (S08IICV2)
11.3.2 IIC Frequency Divider Register (IICF)
R
W
Reset
Field
7:6
MULT
5:0
ICR
7
6
5
4
3
2
1
0
MULT
ICR
0
0
0
0
0
0
0
0
Figure 11-6. IIC Frequency Divider Register (IICF)
Table 11-3. IICF Field Descriptions
Description
IIC Multiplier Factor — The MULT bits define the multiplier factor mul. This factor is used along with the SCL
divider to generate the IIC baud rate. The multiplier factor mul as defined by the MULT bits is provided below.
00 mul = 01
01 mul = 02
10 mul = 04
11 Reserved
IIC 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 IIC baud rate, the SDA hold time, the SCL Start hold time and the SCL Stop hold
time. Table 11-4 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 IIC baud rate.
IIC baud rate = bus speed (Hz)/(mul * SCL divider)
Eqn. 11-1
SDA hold time is the delay from the falling edge of SDA (IIC data) to the changing of SDA (IIC data).
SDA hold time = bus period (s) * mul * SDA hold value
Eqn. 11-2
SCL Start hold time is the delay from the falling edge of SDA (IIC data) while SCL is high (Start condition) to the
falling edge of SCL (IIC clock).
SCL Start hold time = bus period (s) * mul * SCL Start hold value
Eqn. 11-3
SCL Stop hold time is the delay from the rising edge of SCL (IIC clock) to the rising edge of SDA
SDA (IIC data) while SCL is high (Stop condition).
SCL Stop hold time = bus period (s) * mul * SCL Stop hold value
Eqn. 11-4
For example if the bus speed is 8MHz, the table below shows the possible hold time values with different
ICR and MULT selections to achieve an IIC baud rate of 100kbps.
MULT
0x2
0x1
0x1
0x0
0x0
ICR
0x00
0x07
0x0B
0x14
0x18
SDA
3.500
2.500
2.250
2.125
1.125
Hold times (µs)
SCL Start
4.750
4.250
4.000
4.000
3.000
SCL Stop
5.125
5.125
5.250
5.250
5.500
MC9S08SG8 MCU Series Data Sheet, Rev. 0
164
PRELIMINARY
Freescale Semiconductor