M. Amer Iqbal Qureshi
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- Điều hướng trang này:
- MCLR , Master Clear
- Analog and Digital Data
- BASIC CONCEPTS
| Power Supply
PIC microcontrollers use TTL logic, and therefore expect a well regulated 5V power supply. The supply may however range from 3.5V to 5.5V. These microcontrollers require very small amount of current. Indeed these devices have been labeled as nano-watt technology devices. The logical levels are also same, a signal from 0 to about 2V is considered as logical ‘0’ and a signal from 3.5V to 4.5V is considered as logical ‘1’. In order to communicate with devices using higher logical voltages, consider level conversion. MCLR , Master Clear On every PIC microcontroller you will find a pin labeled as MCLR. This pin has two basic functions. It is Fig-2 Showing Pin Outs of PIC-16F877 Microcontroller Fig-3 wiring MCLR Pin Teach Yourself PIC Microcontrollers | www.electronicspk.com | 11 used to reset the microcontroller, like soft-boot. As well as to put the microcontroller into programming mode. The MCLR pin when connected to ground, will reset the microcontroller, and keep it in reset state, till the ground connection is released. After that the microcontroller will have all its RAM reset, and program execution will begin, just like the system has been just powered on. A 10K pull up resistor is usually connected with the pin, to keep it high when reset switch is released. The same pin will also work as program mode pin. When a new software is to be downloaded into the microchip, about 12V are applied to the MCLR pin, by your programming device. This can be done right in your circuit, or by taking the IC out of circuit and putting it into the IC socket on your programmer. We shall talk more about this in section on programming. The 10K resistor is then useful to avoid 12V reaching VCC and therefore to other devices. Analog and Digital Data Our microprocessors use digital data to represent everything. Even music, videos and images all are represented as digital data, which is a series of logical ‘0’ and ‘1’. However our real world data is not digital. It is rather analog. It is rightly said, “We live in an analog world, but process the data in digital world”. Real world data like light, temperature, pressure, heat, height, distance, speed, force etc. all are analog data. In order to utilize these data we have to acquire them with specific sensors or transducers and then convert into digital format for use within microprocessor’s digital world. Many other microcontrollers require an external ADC chip to implement this, however this feature has been nicely built into PIC microcontrollers. The number of Analog channels will vary among devices and some devices will not have this feature on-board. Pins labeled as AN0, AN1 etc are for analog data if required, however they can also function as normal digital pins to work with digital data. As previously said this selection is made by configuring specific registers in microcontroller. BASIC CONCEPTS Did you know that all people can be classified into one of 10 groups- those who are familiar with binary number system and those who are not familiar with it. You don’t understand? That means that you still belong to the later group. If you want to change your status read the following text. Text describing briefly some of the basic concepts used further in this book (just to be sure that we discuss the same issues). tải về 3.06 Mb. Chia sẻ với bạn bè của bạn:
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