Datasheet

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ST7LITE20F2 ST7LITE25F2 ST7LITE29F2 On-chip peripherals
169
11.3.3 Functional description
Timebase counter 1
The 8-bit value of Counter 1 cannot be read or written by software. After an MCU reset, it
starts incrementing from 0 at a frequency of f
OSC
/32. An overflow event occurs when the
counter rolls over from F9h to 00h. If f
OSC
= 8 MHz, then the time period between two
counter overflow events is 1 ms. This period can be doubled by setting the TB bit in the
LTCSR1 register.
When Counter 1 overflows, the TB1F bit is set by hardware and an interrupt request is
generated if the TB1IE bit is set. The TB1F bit is cleared by software reading the LTCSR1
register.
Input capture
The 8-bit input capture register is used to latch the free-running upcounter (Counter 1) 1
after a rising or falling edge is detected on the LTIC pin. When an input capture occurs, the
ICF bit is set and the LTICR1 register contains the MSB of Counter 1. An interrupt is
generated if the ICIE bit is set. The ICF bit is cleared by reading the LTICR register.
The LTICR is a read-only register and always contains the data from the last input capture.
Input capture is inhibited if the ICF bit is set.
Timebase counter 2
Counter 2 is an 8-bit autoreload upcounter. It can be read by accessing the LTCNTR
register. After an MCU reset, it increments at a frequency of f
OSC
/32 starting from the value
stored in the LTARR register. A counter overflow event occurs when the counter rolls over
from FFh to the LTARR reload value. Software can write a new value at anytime in the
LTARR register, this value will be automatically loaded in the counter when the next overflow
occurs.
When Counter 2 overflows, the TB2F bit in the LTCSR2 register is set by hardware and an
interrupt request is generated if the TB2IE bit is set. The TB2F bit is cleared by software
reading the LTCSR2 register.
Figure 41. Input capture timing diagram
04h
8-bit COUNTER 1
t
01h
f
OSC
/32
xxh
02h 03h 05h 06h 07h
04h
LTIC PIN
ICF FLAG
LTICR REGISTER
CLEARED
4µs
(@ 8MHz f
OSC
)
f
CPU
BY S/W
07h
READING
LTIC REGISTER