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CHAPTER 12 U-TIMER (16-bit Timer for UART Baud Rate Generation)
12.3
Description of Operation
This section explains calculation of U-TIMER baud rate and cascade mode.
■ Calculation of Baud Rate
The UART uses the underflow flip-flop (f.f. in the block diagram) of the corresponding U-TIMER
(U-TIMER0 -> UART0, U-TIMER1 -> UART1, U-TIMER2 -> UART2) as the clock source for baud
rates.
• Asynchronous (start-stop) mode
The UART uses the U-TIMER output divided by 16.
UCC1=0
UCC1=1
Maximum bps 33 MHz 515625 bps
• CLK synchronous mode
UCC1=0
bps =
UCC1=1
bps =
Maximum bps 33 MHz 4125000 bps
■ Cascade Mode
Channels 0 and 1 of the U-TIMER can be used in cascade mode.
Example: When UTIMR ch0 is set to "0003
φ
00
UTIM ch0
f.f. ch0
0002
UTIM ch1
f.f. ch1
302
φ
bps =
(2n+2) × 16
φ
bps =
(2n+3) × 16
φ
(2n+2)
φ
(2n+3)
03
02
01
00
03
H
H
H
H
H
H
0001
H
n
--- UTIMR (reload value)
φ
--- Peripheral machine clock frequency
(varies depending on the gear)
n
--- UTIMR (reload value)
(set n=3 or higher number)
φ
--- Peripheral machine clock frequency
(varies depending on the gear)
" and UTIMR ch1 is set to "0100
H
02
01
00
03
02
01
H
H
H
H
H
H
H
"
H
00
03
02
01
00
03
H
H
H
H
H
H
0000
H
02
01
H
H
0100
H
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