Книга: Advanced PIC Microcontroller Projects in C

1.16 Negative Numbers

1.16 Negative Numbers

The most significant bit of a binary number is usually used as the sign bit. By convention, for positive numbers this bit is 0, and for negative numbers this bit is 1. Figure 1.5 shows the 4-bit positive and negative numbers. The largest positive and negative numbers are +7 and –8 respectively.

Figure 1.5: 4-bit positive and negative numbers

To convert a positive number to negative, take the complement of the number and add 1. This process is also called the 2’s complement of the number.

Write decimal number ?6 as a 4-bit number.

First, write the number as a positive number, then find the complement and add 1:

0110 +6

1001 complement

   1 add 1

????
1010 which is ?6

Write decimal number ?25 as a 8-bit number.

First, write the number as a positive number, then find the complement and add 1:

00011001 +25

11100110 complement

       1 add 1

–––––––-
11100111 which is ?25

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