AM186ES Advanced Micro Devices, AM186ES Datasheet - Page 30

• Manufacturer Part Number: AM186ES
• Description: microcontrollers provide a low-cost/ high-performance solution for embedded system designers who wish to use the x86 architecture.
• Manufacturer: Advanced Micro Devices

2.5
Table 2-2
2.6
2-8
SEGMENTS
The Am186ES and Am188ES use four segment registers:
1. Data Segment (DS): The processor assumes that all accesses to the program’s
2. Code Segment (CS): This 64K space is the default location for all instructions. All code
3. Stack Segment (SS): The processor uses the SS register to perform operations that
4. Extra Segment (ES): Usually this segment is used for large string operations and for
When a segment is not defined for a data movement instruction, it’s assumed to be a data
segment. An instruction prefix can be used to override the segment register. For speed
and compact instruction encoding, the segment register used for physical address
generation is implied by the addressing mode used (see Table 2-2).
Segment Register Selection Rules
DATA TYPES
The Am186ES and Am188ES microcontrollers directly support the following data types:
External Data (Global)
Memory Reference
variables are from the 64K space pointed to by the DS register. The data segment holds
data, operands, etc.
must be executed from the code segment.
involve the stack, such as pushes and pops. The stack segment is used for temporary
space.
large data structures. Certain string instructions assume the extra segment as the
segment portion of the address. The extra segment is also used (by using segment
override) as a spare data segment.
Integer—A signed binary numeric value contained in an 8-bit byte or a 16-bit word. All
operations assume a two’s complement representation.
Ordinal—An unsigned binary numeric value contained in an 8-bit byte or a 16-bit word.
Double Word—A signed binary numeric value contained in two sequential 16-bit
addresses, or in a DX::AX register pair.
Quad Word—A signed binary numeric value contained in four sequential 16-bit
addresses.
BCD—An unpacked byte representation of the decimal digits 0–9.
ASCII—A byte representation of alphanumeric and control characters using the ASCII
standard of character representation.
Packed BCD—A packed byte representation of two decimal digits (0–9). One digit is
stored in each nibble (4 bits) of the byte.
Instructions
Local Data
Needed
Stack
Segment Register
Stack (SS)
Code (CS)
Extra (ES)
Data (DS)
Used
Programming
All data references
Instructions (including immediate data)
All stack pushes and pops
Any memory references that use the BP register
All string instruction references that use the DI
register as an index
Implicit Segment Selection Rule