12 8-BIT TIMER (T8F)
12-4
EPSON
S1C17704 TECHNICAL MANUAL
12.4 8-bit Timer Reload Register and Underflow Period
The Reload Data (T8F_TR) Register (0x4202) is used to set the initial value to the down counter.
The counter initial value set in the reload data register is preset to the down counter when the 8-bit timer is reset or
when the counter underflows. When starting the 8-bit timer after resetting, the timer counts down from the reload
value. So the reload value and the input clock frequency determine the period of time from starting the timer until
an underflow occurs (and between underflows). This makes it possible to obtain a desired wait time, a periodical
interrupt interval, or programmable transfer clock for the serial interface.
One-shot mode
Counter
Repeat mode
Counter
0
1
n-1
n
n
Preset by resetting the timer
Preset by resetting the timer
Preset automatically
Underflow
Preset automatically
(n = Reload data)
0
1
n-1
n
n
Underflow
Timer starts
Timer starts
Preset automatically
0
1
n-1
n
Underflow
Figure 12.4.1 Preset Timing
The underflow period is calculated by the expression below.
1
clk_in
Underflow period = —————— [s]
Underflow cycle = —————— [Hz]
clk_in
1
clk_in:
Count clock (prescaler output clock) frequency [Hz]
T8F_TR: Reload data (0–255)
Note
: The UART divides the 8-bit timer output by 16 to generate the sampling clock. Make sure of the
division ratio when setting a transfer rate.
Содержание S1C17704
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