Hardware Reference
In-Depth Information
Figure 1.6
Process of forming a 20-bit physical address
Table 1.6
Contents of the 8086 registers after a reset
Register
Contents (hex.)
Flag
0002
Instruction Pointer
FFF0
Code Segment
F000
Data Segment
0000
Extra Segment
0000
Stack Segment
0000
a power-on or hardware reset, execution commences from address FFFF0 with
a jump to the initial program loader.
80286, 80386, and 80486 processors
Intel's 80286 CPU was first employed in the PC-AT and PS/2 Models 50 and 60.
The 80286 offers a 16 MB physical addressing range but incorporates memory
management capabilities that can map up to a gigabyte of virtual memory.
Depending upon the application, the 80286 is up to six times faster than the
standard 5 MHz 8086 while providing upward software compatibility with the
8086 and 8088 processors.
The 80286 had 15 16-bit registers, of which 14 are identical to those of the
8086. The additional machine status word (MSW) register controls the operating
mode of the processor and also records when a task switch takes place.
The bit functions within the MSW are summarized in Table 1.7. The MSW
is initialized with a value of FFF0H upon reset, the remainder of the 80286
