参数资料
型号: ST72F324K2B3
厂商: STMICROELECTRONICS
元件分类: 微控制器/微处理器
英文描述: 8-BIT, FLASH, 8 MHz, MICROCONTROLLER, PDIP32
封装: 0.400 INCH, SHRINK, PLASTIC, DIP-32
文件页数: 120/156页
文件大小: 1012K
代理商: ST72F324K2B3
ST72324J/K
66/156
16-BIT TIMER (Cont’d)
10.3.3.5 One Pulse Mode
One Pulse mode enables the generation of a
pulse when an external event occurs. This mode is
selected via the OPM bit in the CR2 register.
The one pulse mode uses the Input Capture1
function and the Output Compare1 function.
Procedure:
To use one pulse mode:
1. Load the OC1R register with the value corre-
sponding to the length of the pulse (see the for-
mula in the opposite column).
2. Select the following in the CR1 register:
– Using the OLVL1 bit, select the level to be ap-
plied to the OCMP1 pin after the pulse.
– Using the OLVL2 bit, select the level to be ap-
plied to the OCMP1 pin during the pulse.
– Select the edge of the active transition on the
ICAP1 pin with the IEDG1 bit (the ICAP1 pin
must be configured as floating input).
3. Select the following in the CR2 register:
– Set the OC1E bit, the OCMP1 pin is then ded-
icated to the Output Compare 1 function.
– Set the OPM bit.
– Select the timer clock CC[1:0] (see Table 16
Clock Control Bits).
Then, on a valid event on the ICAP1 pin, the coun-
ter is initialized to FFFCh and OLVL2 bit is loaded
on the OCMP1 pin, the ICF1 bit is set and the val-
ue FFFDh is loaded in the IC1R register.
Because the ICF1 bit is set when an active edge
occurs, an interrupt can be generated if the ICIE
bit is set.
Clearing the Input Capture interrupt request (i.e.
clearing the ICF
i bit) is done in two steps:
1. Reading the SR register while the ICF
i bit is set.
2. An access (read or write) to the IC
iLR register.
The OC1R register value required for a specific
timing application can be calculated using the fol-
lowing formula:
Where:
t
= Pulse period (in seconds)
fCPU
= CPU clock frequency (in hertz)
PRESC = Timer prescaler factor (2, 4 or 8 depend-
ing on the CC[1:0] bits, see Table 16
Clock Control Bits)
If the timer clock is an external clock the formula is:
Where:
t
= Pulse period (in seconds)
fEXT
= External timer clock frequency (in hertz)
When the value of the counter is equal to the value
of the contents of the OC1R register, the OLVL1
bit is output on the OCMP1 pin, (See Figure 50).
Notes:
1. The OCF1 bit cannot be set by hardware in one
pulse mode but the OCF2 bit can generate an
Output Compare interrupt.
2. When the Pulse Width Modulation (PWM) and
One Pulse Mode (OPM) bits are both set, the
PWM mode is the only active one.
3. If OLVL1=OLVL2 a continuous signal will be
seen on the OCMP1 pin.
4. The ICAP1 pin can not be used to perform input
capture. The ICAP2 pin can be used to perform
input capture (ICF2 can be set and IC2R can be
loaded) but the user must take care that the
counter is reset each time a valid edge occurs
on the ICAP1 pin and ICF1 can also generates
interrupt if ICIE is set.
5. When one pulse mode is used OC1R is dedi-
cated to this mode. Nevertheless OC2R and
OCF2 can be used to indicate a period of time
has been elapsed but cannot generate an out-
put waveform because the level OLVL2 is dedi-
cated to the one pulse mode.
event occurs
Counter
= OC1R
OCMP1 = OLVL1
When
on ICAP1
One pulse mode cycle
OCMP1 = OLVL2
Counter is reset
to FFFCh
ICF1 bit is set
ICR1 = Counter
OC
iR Value =
t * fCPU
PRESC
-5
OC
iR=
t * fEXT -5
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