Fujitsu FR81S User Manual
CHAPTER 40: MULTI-FUNCTION SERIAL INTERFACE
6. Operation of CSIO
FUJITSU SEMICONDUCTOR LIMITED
CHAPTER : MULTI-FUNCTION SERIAL INTERFACE
FUJITSU SEMICONDUCTOR CONFIDENTIAL
238
6.2.8. Baud Rate Generation
The dedicated baud rate generator works only in master operation. However, if the reception FIFO is to be
used, set the dedicated baud rate generator even in slave operation.
The dedicated baud rate generator settings are different between the master and slave operations.
[1] Master operation
⋅
The dedicated baud rate generator divides the internal clock and a baud rate is selected.
⋅
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 internal clock with the setting value.
[2] Slave operation
⋅
The dedicated baud rate generator does not work in slave operation (SCR:MS=1). (The external clock
entered from the clock input pin SCK is used without change.)
Note:
If the reception FIFO is to be used, set the dedicated baud rate generator even in slave operation.
Baud Rate Calculation
Set two 15-bit reload counters in the baud rate generator register (BGR). The baud rate calculation formulas
are as follows:
(1) Reload value
V
=
φ
: b
−
1
V: Reload value φ: bus clock frequency b: Baud rate
(2) Example of calculation
Reload values when setting the bus clock frequency at 16 MHz, usage of internal clock, and baud rate at
19200 bps are as follows:
Reload value:
V = (16 ∗ 1,000,000) / 19200 − 1 = 832
Therefore, the baud rate is
b = (16
∗
1,000,000) / (832+1) = 19208 bps
(3) Baud rate error
The baud rate error can be obtained using the following formula:
Error (%) = (calculated value − desired value) / desired value ∗ 100
(Example) When you set bus clock at 20 MHz and target baud rate at 153600 bps:
Reload value = (20 ∗ 1,000,000) / 153600 − 1 = 129
Baud rate (calculated) = (20 ∗ 1,000,000) / (129 + 1) = 153846 bps
Error (%) = (153846 ∗ 153600) / 153600 ∗ 100 = 0.16(%)
MB91520 Series
MN705-00010-1v0-E
1551