ST72325XXX Datasheet, PDF (109/243 Pages) STMicroelectronics – SCI asynchronous serial interface

ST72325xxx-Auto
16-bit timer
13.3.4
Output compare
In this section, the index, i, may be 1 or 2 because there are two output compare functions in
the 16-bit timer.
This function can be used to control an output waveform or indicate when a period of time
has elapsed.
When a match is found between the Output Compare register and the free running counter,
the output compare function:
● Assigns pins with a programmable value if the OCiE bit is set
● Sets a flag in the status register
● Generates an interrupt if enabled
Two 16-bit registers Output Compare Register 1 (OC1R) and Output Compare Register 2
(OC2R) contain the value to be compared to the counter register each timer clock cycle.
MS byte
LS byte
OCiR
OCiHR
OCiLR
t(s) ^{These registers are readable and writable and are not affected by the timer hardware. A}
c ^{reset event changes the OCiR value to 8000h.}
du ^{Timing resolution is one count of the free running counter: (fCPU/CC[1:0]).}
ro _Procedure
P _{To use the output compare function, select the following in the CR2 register:}
lete ^{● Set the OCiE bit if an output is needed then the OCMPi pin is dedicated to the output}
compare i signal.
so _{● Select the timer clock (CC[1:0]) (see Table 62: Timer clock selection).}
Ob ^{And select the following in the CR1 register:}
- _{● Select the OLVLi bit to applied to the OCMPi pins after the match occurs.}
t(s) ^{● Set the OCIE bit to generate an interrupt if it is needed.}
When a match is found between OCRi register and CR register:
uc _{● OCFi bit is set.}
rod ^{● The OCMPi pin takes OLVLi bit value (OCMPi pin latch is forced low during reset).}
● A timer interrupt is generated if the OCIE bit is set in the CR1 register and the I bit is
P _{cleared in the CC register (CC).}
te_{The OCiR register value required for a specific timing application can be calculated using}
le_{the following formula:}
bso ^{ OCiR = t * fCPU}
O ^PRESC
Where:
t
= Output compare period (in seconds)
f_CPU = CPU clock frequency (in hertz)
PRESC = Timer prescaler factor (2, 4 or 8 depending on CC[1:0] bits; see Table 62:
Timer clock selection)
Doc ID 13770 Rev 3
109/243