![]() ![]() The instruction cycle is the basic unit of time in every PIC program – all other time delays are measured in multiples of it. When the PIC runs at a higher clock speed it performs more computations per second, but it also consumes more power. In simple terms, the choice of clock speed boils down to a trade-off between computing power and energy efficiency. If precision timing is a priority, an external crystal oscillator is often used. However, an external clock source can also be used. The clock signal is often provided by the internal RC oscillator, which requires no additional hardware components, and which can be configured to run at a range of frequencies (the default is 1MHz). ![]() Typical values range from tens of kHz to tens of MHz. The PIC18F4620 can use a very wide range of clock frequencies. When the clock signal is provided by the PIC’s internal RC oscillator, and assuming the oscillator frequency (Tosc) is not changed from its default value of 1MHz, then the clock period (Tosc) is 1us and the instruction cycle (Tcy) is 4μs. The PIC18F4620 (like many other PIC microcontrollers) performs one machine code instruction every four clock cycles. Different processor architectures require a different number of clock cycles to perform each machine code instruction. Every microprocessor uses a clock signal (basically a square wave signal) to pace its operation. The basic unit of time in every program that runs on a PIC18F4620 is the instruction cycle, which is the time taken to execute one machine code instruction. In this post, I will describe the timing on the PIC18F4620 microcontroller. It’s slightly different on each device, but the fundamentals are generally more or less the same. ![]() One of the most important things to understand when programming a microcontroller is how the timing works. ![]()
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