mc9s08gt32a Freescale Semiconductor, Inc, mc9s08gt32a Datasheet - Page 208

• Manufacturer Part Number: mc9s08gt32a
• Description: Hcs08 Microcontrollers 8-bit Microcontroller Family
• Manufacturer: Freescale Semiconductor, Inc

208
MULT
Field
ICR
7:6
5:0
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 are used to
define the SCL divider and the SDA hold value. The SCL divider multiplied by the value provided by the MULT
register (multiplier factor mul) is used to generate IIC baud rate.
SDA hold time is the delay from the falling edge of the SCL (IIC clock) to the changing of SDA (IIC data). The ICR
is used to determine the SDA hold value.
Table 13-3
be used to set IIC baud rate and SDA hold time. For example:
Table 13-3
hold value of 9.
If the generated SDA hold value is not acceptable, the MULT bits can be used to change the ICR. This will result
in a different SDA hold value.
IIC baud rate = bus speed (Hz)/(mul * SCL divider)
SDA hold time = bus period (s) * SDA hold value
Bus speed = 8 MHz
MULT is set to 01 (mul = 2)
Desired IIC baud rate = 100 kbps
IIC baud rate = bus speed (Hz)/(mul * SCL divider)
100000 = 8000000/(2*SCL divider)
SCL divider = 40
SDA hold time = bus period (s) * SDA hold value
SDA hold time = 1/8000000 * 9 = 1.125 μs
provides the SCL divider and SDA hold values for corresponding values of the ICR. These values can
shows that ICR must be set to 0B to provide an SCL divider of 40 and that this will result in an SDA
Table 13-2. IIC1F Register Field Descriptions
MC9S08GB60A Data Sheet, Rev. 1.02
Description
Freescale Semiconductor