The clock from the selected source is input to the AVR clock generator, and routed to the appropriate As found in the datasheet, ATMega8 has the following clock source options, selectable by Flash Fuse Bits as shown in the table below. For all fuses, ‘1’ means unprogrammed, and ‘0’ means programmed. Each of those bits, depending on whether they are on or off, impacts the critical operations of the microcontroller. So we have just 16 bits to set to on or off. As you may well know, one byte contains 8 bits. Typically, there are only two fuse bytes: a high one, and a low one. You only need to set them once, but if you don’t do this right, get ready to expect a costly disaster! The fuses determine how the chip will act, whether it has a bootloader, what speed and voltage it likes to run at, etc. On the other hand, when precision timing is crucial, we need an alternate method like using suitable crystals, or ceramic resonators.įuses are important when it comes to uC programming, that is why fuses are well-documented in manufactures’ datasheets. If we are writing code for a basic job, the internal clock should suffice. How can we set a clock speed? As said, we have two options use the internal one, or use an external source. Note that the internal ATMega8 clock can be set up to a maximum frequency of 8 MHz, and beyond that you need an external clock source. However, this is not required incase of a ceramic resonator because it is a combination of the crystal and capacitors, built into one compact package. ![]() In practice, it is required to add two ceramic capacitors (usually 22pF value) with the crystal as shown in the next figure. Crystal is a 2-pin component, but ceramic resonator have 3 pins. Ceramic resonator is an alternative to the common crystal. If we need a special clock rate (for example 12MHz) we can use an external crystal or oscillator.Ĭrystals come in different pacakges, with the speed printed on the body, usually in MHz. Literally, ‘ External Clock‘ means that a square wave is being input into the ‘CLOCK-IN’ pin, but this option is rarely used. Having an internal oscillator means we don’t need to wire up an external crystal and hence we can use the clock pins for other tasks. This clock is good for most basic projects, but its not very precise. ‘ Internal Clock‘ means the little oscillator inside the chip. The Clock Source can be either of the following: Every microcontroller chip uses a clock, which keeps track of time for the chip, in general one assembly code instruction is run every clock cycle. If you have multiple hardware devices connected digitally, the Clock Source on one device must be Internal, the 'leader', and all other devices should be set to clock externally, the “follower(s)”.įor more information on which Clock Source to choose, Click Here.You know the basics about how the chip is clocked. If you're only using one device, then you should select its internal clock source. ![]() In a digital system, it's important, each device that's sending signals digitally shares the same clock source, so they can be synchronised. The Clock Source manages how the unit derives its digital clock. The standard CD audio format is 44.1 kHz, and the standard video audio format is 48 kHz. The higher the Sample Rate, the more samples of audio being carried by the device as well as a higher frequency range being captured, meaning the higher the Sample Rate, the higher the quality of audio being recorded. For example, 44,100 samples per second can be written as either 44,100 Hz or 44.1 kHz. The Sample Rate is the number of audio samples carried per second, measured in Hz or kHz (1 kHz being 1,000 Hz).
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