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In computing and in embedded systems, a programmable interval timer (PIT) is a counter that generates an output signal when it reaches a programmed count. The output signal may trigger an interrupt .
In embedded systems and control systems, watchdog timers are often used to activate fail-safe circuitry. When activated, the fail-safe circuitry forces all control outputs to safe states (e.g., turns off motors, heaters, and high-voltages) to prevent injuries and equipment damage while the fault persists. In a two-stage watchdog, the first ...
RTC_A/B are 32-bit hardware counter modules that provide clock counters with a calendar, a flexible programmable alarm, and calibration. The RTC_B includes a switchable battery backup system that provides the ability for the RTC to operate when the primary supply fails. 16-bit timers; Timer_A, Timer_B and Timer_D are asynchronous 16-bit timers ...
Modulus counter – counts through a particular number of states. Decade counter – modulus ten counter (counts through ten states). Up/down counter – counts up and down, as directed by a control input, or by the use of separate "up" and "down" clocks. Ring counter – formed by a "circular" shift register. Johnson counter – a twisted ring ...
Currently produced by NXP, the 2691 [10] is a single channel UART that also includes a programmable counter/timer. The 2691 has a single-byte transmitter holding register and a 4-byte receive FIFO. Maximum standard speed of the 2692 is 115.2 kbit/s.
A prescaler is an electronic counting circuit used to reduce a high frequency electrical signal to a lower frequency by integer division.The prescaler takes the basic timer clock frequency (which may be the CPU clock frequency or may be some higher or lower frequency) and divides it by some value before feeding it to the timer, according to how the prescaler register(s) are configured.
An alternative design uses a counter with a sufficiently large word size that it will not reach its overflow limit before the end of life of the system. More sophisticated timers may have comparison logic to compare the timer value against a specific value set by software, which triggers some action when the timer value matches the preset value.
This frequency, divided by 2 16 (the largest divisor the 8253 is capable of) produces the ≈18.2 Hz timer interrupt used in MS-DOS and related operating systems. In the original IBM PCs, Counter 0 is used to generate a timekeeping interrupt. Counter 1 is used to trigger the refresh of DRAM memory. Counter 2 is used to generate tones via the PC ...
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