Fujitsu FR81S User Manual
CHAPTER 40: MULTI-FUNCTION SERIAL INTERFACE
8. Operation of I2C
FUJITSU SEMICONDUCTOR LIMITED
CHAPTER : MULTI-FUNCTION SERIAL INTERFACE
FUJITSU SEMICONDUCTOR CONFIDENTIAL
330
8.2.6. Baud Rate Generation
The dedicated baud rate generator sets a serial clock frequency.
Baud Rate Selection
Baud rate obtained when a dedicated baud rate generator (reload counter)
divides the frequency of the internal clock
There are two internal reload counters that correspond to the transmission and reception serial clocks,
respectively. The baud rate can be selected by setting a 15-bit reload value in the baud rate generator
register (BGR). The reload counter divides the frequency of the internal clock by the specified value.
Baud Rate Calculation
The two 15-bit reload counters are set using the baud rate generator register (BGR). The baud rate
calculation formulas are as follows:
(1) Reload value
V = φ / b - 1
V: Reload value b: Baud rate φ: Internal clock (peripheral clock (PCLK)) frequency
However, the specified baud rate may not be generated depending on the rising time of SCL on the I2C bus.
Adjust the reload value as required.
(2) Example of calculation
The reload value is as follows if the bus clock is 16MHz and the baud rate is to be 400kbps:
Reload value:
V = (16 × 1,000,000) / 400,000 - 1 = 39
Therefore, the baud rate is
b = (16 × 1,000,000) / (38+2) = 400kbps
Notes:
⋅
Write to the baud rate generator (BGR) in 16-bit access mode.
⋅
Configure the baud rate generator register when the ISMK:EN bit is "0".
⋅
Bus clock should be set with 8MHz or more in operating mode 4 (I
2
C mode) and baud rate generator
configured in 400kbps or more should not be used.
⋅
Set the reload value to "0" to stop the reload counter.
MB91520 Series
MN705-00010-1v0-E
1643