Interfacing PIC Microcontrollers 13. Explore in detail microcontroller interfacing techniques using the popular PIC 16F877 Work through step-by-step examples interactively using circuit simulation software, supplied as assembly source code Gain the knowledge of a wide range of peripheral devices such as keyboards, displays, sensors and drives and serial communication with other processors, memory and more Use interactive simulation software to design and test circuits. | Interfacing PIC Microcontrollers However as numbers get bigger and smaller the number of bits needed will be excessive. An alternative format is needed to represent large and small numbers. On a calculator scientific notation is used base 10. For example X 1073 is a large number X 10 23 is a small one. The decimal part is called the mantissa and the range multiplier the exponent. Computers work in base 2 so an example of a large negative number could be X 210011 and a small positive one X 2 01001. We have to decide on the number of bits to use which in turn determines the precision and range of the number itself. 32-bit numbers are sufficient for most purposes but the bits available must be allocated in groups as mantissa sign exponent and exponent sign. This gives the FP numerical type meaning the decimal point can move according to the exponent . Standard forms use 1 bit to represent the sign 23 bits for the mantissa and 8 bits for the exponent and its sign. To illustrate the form of a floating-point number the conversion of this type into decimal will be detailed in section Floating Point . Conversion Conversion between numerical types is often required in microprocessor systems. Data may be input in ASCII processed in binary or FP format and output in BCD. Machine code is normally displayed in hexadecimal since binary is cumbersome so we need to know how to perform this conversion. FP formats are needed to extend the range and precision of numerical data. Binary to Decimal The structure of binary numbers has been described above. The value of a number is found by multiplying each digit by its decimal column weight and adding. The weighting of the digits in binary is from the LSB 1 2 4 8 16 . or 20 21 22 23 . that is the base of the number system is raised to the power 1 2 3 . The conversion process for a sample 8-bit binary number is therefore 1001 01102 128 X 1 64 X 0 32 X 0 16 X 1 8 X 0 4 X 1 2 X 1 1 X 0 128 16 4 2 15010
