Intel 80287, 80286 manual Ascii

80286 BASE ARCHITECTURE

Ordinal:

An unsigned binary numeric value contained in an 8-bit byte or 16-bit word.

Pointer:

A 32-bit address quantity composed of a segment selector component and an offset component. Each component is a 16-bit word.

String:

A contiguous sequence of bytes or words. A string may contain from 1 byte to 64K bytes.

ASCII:

A byte representation of alphanumeric and control characters using the. ASCII standard of character representation.

BCD:

A byte (unpacked) representation of the decimal digits (0-9).

Packed BCD:

A byte (packed) representation of two decimal digits (0-9). One digit is stored in each nibble of the byte.

Floating Point:

A signed 32-, 64-, or 80-bit real number representation. (Floating operands are supported using the 80287 Numeric Processor Configuration.)

Figure 2-3 graphically represents the data types supported by the 80286. 80286 arithmetic operations may be performed on five types of numbers: unsigned binary, signed binary (integers), unsigned pflcked decimal, unsigned unpacked decimal, and floating point. Binary numbers may be 8 or 16 bits long. Decimal numbers are stored in bytes; two digits per byte for packed decimal, one digit per byte for unpacked decimal. The processor always assumes that the operands specified in arithmetic instructions contain data that represent valid numbers for the type of instruction being performed. Invalid data may produce unpredictable results.

Unsigned binary numbers may be either 8 or 16 bits long; all bits are considered in determining a number's magnitude. The value range of an 8-bit unsigned binary number is 0-255; 16 bits can repre- sent values from 0 through 65,535. Addition, subtraction, multiplication and division operations are available for unsigned binary numbers.

Signed binary numbers (integers) may be either 8 or 16 bits long. The high-order (leftmost) bit is interpreted as the number's sign: O=positive and 1= negative. Negative numbers are represented in standard two's complement notation. Since the high-order bit is used for a sign, the range of an 8-bit integer is -128 through +127; 16-bit integers may range from -.32,768 through +32,767. The value zero has a positive sign.

2-4