Obsolete
Product(s)
- Obsolete
Product(s)
ST72324B-Auto
On-chip peripherals
The OC1R register value required for a specific timing application can be calculated using
the following formula:
Where:
t
= Pulse period (in seconds)
fCPU
= CPU clock frequnency (in hertz)
PRESC = Timer prescaler factor (2, 4 or 8 depending on the CC[1:0] bits; see
Table 50)
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 45).
Note:
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 dedicated to this mode. Nevertheless OC2R and
OCF2 can be used to indicate a period of time has been elapsed but cannot generate an
output waveform because the level OLVL2 is dedicated to the one pulse mode.
Figure 45.
One Pulse mode timing example(1)
1.
IEDG1 = 1, OC1R = 2ED0h, OLVL1 = 0, OLVL2 = 1
OCiR value =
t * fCPU
PRESC
- 5
OCiR = t * fEXT - 5
Counter
FFFC FFFD FFFE
2ED0
2ED1 2ED2
2ED3
FFFC FFFD
OLVL2
OLVL1
ICAP1
OCMP1
Compare1
01F8
2ED3
IC1R