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NUMBER CRUNCHING WITH EMBEDDED PROCESSORS

by George Martin

Start ı The Unsigned Modifier in Action ı The Signed Notation ı A Lesson in Subtraction ı Sources and PDF

This month, letıs talk numbersıbinary numbers, embedded processors, and how different numbering systems interact with CPU instructions and the C programming language.

NUMBER TYPES IN C

The C language has some built-in number typesıchar, int, long, and float, along with modifiers, signed, unsigned, short, and double. These number types have different meanings, depending on the compiler and CPU. After I define the basic number types, Iıll focus on signed and unsigned.

Itıs good practice to use #typedefs, so youıre sure about the amount of data you are referencing. Letıs assume you are writing code for an 8-bit CPU, and your compiler defines char as 8 bits, int as 16 bits, and long as 32 bits. Table 1 shows how the typefdefs would look.

BINARY BASICS

Letıs see how the CPU works with binary numbers. The experts may wish to skip ahead, but letıs assume you have an 8-bit computer with a basic 8-bit register. An 8-bit register can hold the binary patterns from 0000 0000 to 1111 1111. In a straightforward notation, 0000 0000 represents 0 decimal and 1111 1111 represents 255 decimals. In C, this is called the unsigned modifier.

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