Chapter 14 80386 Real-Address Mode

The real-address mode of the 80386 executes object code designed for execution on 8086, 8088, 80186, or 80188 processors, or for execution in the real-address mode of an 80286:

In effect, the architecture of the 80386 in this mode is almost identical to that of the 8086, 8088, 80186, and 80188. To a programmer, an 80386 in real-address mode appears as a high-speed 8086 with extensions to the instruction set and registers. The principal features of this architecture are defined in Chapters 2 and 3.

This chapter discusses certain additional topics that complete the system programmer's view of the 80386 in real-address mode:

• Address formation.
• Extensions to registers and instructions.
• Interrupt and exception handling.
• Entering and leaving real-address mode.
• Real-address-mode exceptions.
• Differences from 8086.
• Differences from 80286 real-address mode.

• 14.1 Physical Address Formation
• 14.2 Registers and Instructions
• 14.3 Interrupt and Exception Handling
• 14.4 Entering and Leaving Real-Address Mode
• 14.4.1 Switching to Protected Mode
• 14.5 Switching Back to Real-Address Mode
• 14.6 Real-Address Mode Exceptions
• 14.7 Differences From 8086
• 14.8 Differences From 80286 Real-Address Mode
• 14.8.1 Bus Lock
• 14.8.2 Location of First Instruction
• 14.8.3 Initial Values of General Registers
• 14.8.4 MSW Initialization

• Figure 14-1. Real-Address Mode Address Formation

• Table 14-1. 80386 Real-Address Mode Exceptions
• Table 14-2. New 80386 Exceptions