C8051F045 查看數據表（PDF） - Silicon Laboratories
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C8051F045 Datasheet PDF : 328 Pages
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C8051F040/1/2/3/4/5/6/7
23.2.3. Auto-Reload Mode
In Auto-Reload Mode, the counter/timer can be configured to count up or down and cause an interrupt/flag
to occur upon an overflow/underflow event. When counting up, the counter/timer will set its overflow/under-
flow flag (TFn) and cause an interrupt (if enabled) upon overflow/underflow, the values in the Reload/Cap-
ture Registers (RCAPnH and RCAPnL) are loaded into the timer, and the timer is restarted. When the
Timer External Enable Bit (EXENn) bit is set to ‘1’ and the Decrement Enable Bit (DCEN) is ‘0’, a ‘1’-to-‘0’
transition on the TnEX pin (configured as an input in the digital crossbar) will cause a timer reload (in addi-
tion to timer overflows causing auto-reloads). When DCEN is set to ‘1’, the state of the TnEX pin controls
whether the counter/timer counts up (increments) or down (decrements), and will not cause an auto-reload
or interrupt event. See Section 23.2.1 for information concerning configuration of a timer to count down.
When counting down, the counter/timer will set its overflow/underflow flag (TFn) and cause an interrupt (if
enabled) when the value in the timer (TMRnH and TMRnL registers) matches the 16-bit value in the
Reload/Capture Registers (RCAPnH and RCAPnL). This is considered an underflow event, and will cause
the timer to load the value 0xFFFF. The timer is automatically restarted when an underflow occurs.
Counter/Timer with Auto-Reload mode is selected by clearing the CP/RLn bit. Setting TRn to logic 1
enables and starts the timer.
In Auto-Reload Mode, the External Flag (EXFn) toggles upon every overflow or underflow and does not
cause an interrupt. The EXFn flag can be thought of as the most significant bit (MSB) of a 17-bit counter.
2
SYSCLK
12
External Clock
(XTAL1)
Tn
8
0
1
Crossbar
TRn
EXENn
TnE
Crossbar
X
TMRnCF
T
n
M
1
T
n
M
0
T
O
G
n
T
n
O
E
D
E
C
E
N
Toggle Logic
0
0xFF
0xFF
1
Tn
(Port Pin)
TCLK TMRnL
OVF
TMRnH
Reload RCAPnL RCAPnH
CP/RLn
C/Tn
TRn
EXENn
EXFn
TFn
Interrupt
Figure 23.5. Tn Auto-reload Mode and Toggle Mode Block Diagram
Rev. 1.5
297
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