M. Amer Iqbal Qureshi
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| Marking numbers
Hexadecimal number system is along with binary and decimal number systems considered to be the most important for us. It is easy to make conversion of any hexadecimal number to binary and it is also easy to remember it. However, these conversions as well as common use of different number systems may cause confusion. For example, what does the statement “It is necessary to count up 110 products on assembly line” actually mean? Depending on whether it is about binary, decimal or hexadecimal system, the result could be 6, 110 or 272 products, respectively! Accordingly, in order to avoid misunderstandings, different prefixes and suffixes are directly added to the numbers. The prefix $ or 0x as well as the suffix h marks the numbers in hexadecimal system. For example, hexadecimal number 10AF may look as follows $10AF, 0x10AF or 10AFh. Similarly, binary numbers usually get the suffix % or 0b, whereas decimal numbers get Fig. 7 Showing Hexadecimal to decimal conversion Teach Yourself PIC Microcontrollers | www.electronicspk.com | 14 the suffix D. Commonly if no suffix is used the number is assumed to be decimal. Bit Theory says a bit is the basic unit of information...Let us neglect such a dry explanation for a moment and take a look at what it is in practice. The answer is- nothing special- a bit is a binary digit. Similar to decimal number system in which digits in a number do not have the same value ( for example digits in the number 444 are the same, but have different values), the “significance” of some bit depends on the position it has in binary number. Therefore, there is no point to talk about units, tens etc. Instead, here it is about zero bit (rightmost bit), first bit (second from the right) etc. In addition, since the binary system uses two digits only (0 and 1), the value of one bit can be 0 or 1. Do not let you be confused if you find some bit has value 4, 16 or 64. It means that bit’s values are represented in decimal system. Simply, we have got so much accustomed to the usage of decimal numbers that these expressions became common. It would be correct to say for example, “the value of the sixth bit in binary number is equivalent to decimal number 64”. But we all are just humans and a habit does its own...Besides, how would it sound “number: one-onezero- one-zero...” Byte A byte or a program word consists of eight bits placed next to each other. If a bit is a digit, it is logical that bytes represent numbers. All mathematical operations can be performed upon them, like upon common decimal numbers. As It is case with digits of any other number, byte digits do not have the same significance. The largest value has the left-most bit called most significant bit (MSB). The right-most bit has the least value and is therefore called least significant bit (LSB). Since eight zeros and units of one byte can be combined in 256 different ways, the largest decimal number which can be represented by one byte is 255 (one combination represents zero). Concerning terminology used in computer science, a concept of nibble should be clarified. Somewhere and somehow, this term referred to as half a byte came up. Depending on which half of the byte we are talking about (left or right), there are “high” and “low” nibbles. tải về 3.06 Mb. Chia sẻ với bạn bè của bạn:
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