13-4
Seiko Epson Corporation
S1C31D50 TECHNICAL MANUAL
(Rev. 1.00)
13.3.
Clock Settings
13.3.1.
UART3 Operating Clock
When using the UART3 Ch.
n
, the UART3 Ch.
n
operating clock CLK_UART3_
n
must be supplied to the
UART3 Ch.
n
from the clock generator. The CLK_UART3_
n
supply should be controlled as in the procedure
shown below.
1.
Enable the clock source in the clock generator if it is stopped (refer to “Clock Generator” in the
“P
ower Supply
, Reset, and Clocks” chapter).
2.
Set the following UART3_
n
CLK register bits:
-
UART3_
n
CLK.CLKSRC[1:0] bits
(Clock source selection)
-
UART3_
n
CLK.CLKDIV[1:0] bits
(Clock division ratio selection = Clock frequency setting)
The UART3 operating clock should be selected so that the baud rate generator will be configured
easily.
13.3.2.
Clock Supply in SLEEP Mode
When using the UART3 during SLEEP mode, the UART3 operating clock CLK_UART3_
n
must be
configured so that it will keep supplying by writing 0 to the CLGOSC.
xxxx
SLPC bit for the CLK_UART3_
n
clock source.
13.3.3.
Clock Supply During Debugging
The CLK_UART3_
n
supply during debugging should be controlled using the UART3_
n
CLK.DBRUN bit.
The CLK_UART3_
n
supply to the UART3 Ch.
n
is suspended when the CPU enters debug state if the
UART3_
n
CLK.DBRUN bit = 0. After the CPU returns to normal mode, the CLK_UART3_
n
supply resumes.
Although the UART3 Ch.
n
stops operating when the CLK_UART3_
n
supply is suspended, the output pin
and registers retain the status before the debug state was entered. If the UART3_
n
CLK.DBRUN bit = 1,
the CLK_UART3_
n
supply is not suspended and the UART3 Ch.
n
will keep operating in a debug state.
13.3.4.
Baud Rate Generator
The UART3 includes a baud rate generator to generate the transfer (sampling) clock. The transfer rate is
determined by the UART3_
n
MOD.BRDIV, UART3_
n
BR.BRT[7:0], and UART3_
n
BR.FMD[3:0] bit settings. Use
the following equations to calculate the setting values for obtaining the desired transfer rate.
𝑏𝑠𝑝 =
𝐶𝐿𝐾_𝑈𝐴𝑅𝑇3
𝐵𝑅𝑇+1
𝐵𝑅𝐷𝐼𝑉
∗ 𝐹𝑀𝐷
𝐵𝑅𝑇 = 𝐵𝑅𝐷𝐼𝑉 × (
𝐶𝐿𝐾_𝑈𝐴𝑅𝑇3
𝑏𝑝𝑠
− 𝐹𝑀𝐷) − 1 (𝐸𝑞. 13.1)
Where
bps: Transfer rate [bit/s]
CLK_UART3: UART3 operating clock frequency [Hz]
BRDIV:
Baud rate division ratio (1/16 or 1/4) * Selected by the UART3_
n
MOD.BRDIV bit
BRT:
UART3_
n
BR.BRT[7:0] setting value (0 to 255)
FMD: UART3_
n
BR.FMD[3:0] setting value (0 to 15)
For the transfer rate range configurable in the UART3, refer to
“
UART Characteristics, Transfer baud
rates U
BRT1
and U
BRT2
”
in the
“Electrical
Characteristics”
chapter.
Summary of Contents for S1C31D50
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