A Detailed Explanation Of The Three Main Types Of Timer Parameters
Jul 17, 2025
1. Time Parameters: The Core Control Dimension of a Timer
Time parameters determine the timer's duty cycle and delay effect, and are divided into two categories:
1. Single-shot delay: After triggering, the action is executed only once, such as the automatic shutdown function of a home appliance. Typical values range from 0.1 milliseconds (such as the STM32 hardware timer) to 999 hours (industrial PLC timing module). Accuracy depends on the clock source (e.g., crystal oscillator error ±50ppm).
2. Cycle period: Repeated triggering at a fixed interval, such as PWM signal generation. Common periods range from 1μs to 1s (refer to the Texas Instruments Tiva series manual) and must match the real-time requirements of the task.
*Extended Note*: For high-precision scenarios (such as medical equipment), a temperature-compensated crystal oscillator (TCXO) is required to maintain an error within ±0.01%. For ordinary home appliances, an RC oscillator circuit (±5% error) can be used.
2. Trigger Mode: Determines the Timer Start Condition
Trigger modes are categorized as hardware and software:
1. Hardware Trigger: Activated by an external signal, for example:
- Edge Trigger (Rising/Falling Edge): Used for motor speed detection, with a response time as fast as 10ns (see Microchip application note AN1257).
- Level Trigger: Continuously time the time while a high/low level is maintained, such as a long-press control in an access control system.
2. Software Trigger: Initiated by program instructions, it offers high flexibility but also has a latency (typically 1-100μs), making it suitable for non-real-time task scheduling.
*Comparative Analysis*: Hardware triggering is suitable for high-speed events (such as ultrasonic ranging), while software triggering is more suitable for predictable logic control.
3. Accuracy Parameters: Key Affecting Timing Reliability
Accuracy is determined by both the clock source and circuit design. Key indicators include:
1. Clock Stability: Temperature changes can cause crystal oscillator frequency drift. For example, oven-controlled crystal oscillators (OCXOs) offer a stability of ±0.001ppm (see the Epson SG-8101 datasheet), but this is relatively expensive.
2. Resolution: The smallest adjustable time unit. A 32-bit timer (such as an ARM Cortex-M) can achieve a resolution of 1/(84MHz) ≈ 11.9ns.
3. Jitter: Signal timing deviation. A high-quality timer has jitter < 1ns (e.g., the Silicon Labs SI5341 datasheet).
*Application Recommendations*: Industrial automation recommends using timer chips with error compensation, while consumer electronics can sacrifice some accuracy to reduce costs.
By properly configuring the above parameters, a timer can adapt to a full range of scenarios, from microsecond-level signal acquisition to hour-level process control. When selecting a timer, consider the trade-offs between cost, accuracy, and response speed. Consult the manufacturer's datasheet for verification.
