On-chip peripherals
ST72344xx, ST72345xx
Input capture
In this section, the index, i, may be 1 or 2 because there are 2 input capture functions in the
16-bit timer.
The two input-capture 16-bit registers (IC1R and IC2R) are used to latch the value of the
free-running counter after a transition detected by the ICAPi pin.
ICiR register is a read-only register.
The active transition is software-programmable through the IEDGi bit of Control Registers
(CRi).
The timing resolution is one count of the free-running counter: (fCPU/CC[1:0]).
Procedure:
To use the input capture function, select the following in the CR2 register:
●
●
Select the edge of the active transition on the ICAP2 pin with the IEDG2 bit (the ICAP2
pin must be configured as floating input).
And select the following in the CR1 register:
●
Set the ICIE bit to generate an interrupt after an input capture coming from either the
ICAP1 pin or the ICAP2 pin
●
Select the edge of the active transition on the ICAP1 pin with the IEDG1 bit (the
ICAP1pin must be configured as floating input).
When an input capture occurs:
●
ICFi bit is set.
●
The ICiR register contains the value of the free running counter on the active transition
●
A timer interrupt is generated if the ICIE bit is set and the I bit is cleared in the CC
register. Otherwise, the interrupt remains pending until both conditions become true.
Clearing the Input Capture interrupt request (i.e. clearing the ICFi bit) is done in two steps:
1.
Reading the SR register while the ICFi bit is set.
2.
An access (read or write) to the ICiLR register.
Note:
1
After reading the ICiHR register, transfer of input capture data is inhibited and ICFi will never
be set until the ICiLR register is also read.
2
The ICiR register contains the free running counter value which corresponds to the most
recent input capture.
3
The 2 input capture functions can be used together even if the timer also uses the 2 output
compare functions.
4
In One-pulse Mode and PWM mode only the input capture 2 can be used.
5
The alternate inputs (ICAP1 & ICAP2) are always directly connected to the timer. So any
transitions on these pins activate the input capture function.
Moreover if one of the ICAPi pin is configured as an input and the second one as an output,
Table 44.
ICiR register
MS Byte
LS Byte
ICiR
ICiHR
ICiLR