Processor System; Address And Data Bus Structure; Software Compatibility; Modes Of Operation - Mitsubishi Electric LS Pro Hardware Technical Reference

3.2

PROCESSOR SYSTEM

The processor system uses either an 80386SX or a 486SLC microprocessor, these are
described below.
80386SX The 80386SX is a high performance microprocessor which features:
processor
features • 24-bit address and 16-bit data busses.
• compatibility with software written for less powerful members of the 80X86
microprocessor family - the 8086, 8088 and 80286.
• high speed.
• enhanced modes of operation - real, protected and virtual 8086 mode.
• on board memory management unit.
486SLC The 486SLC incorporates all the features of the 80386SX listed above. In addition
processor it offers:
features
• 1 Kbyte of cache RAM.
• 80486SX instruction set compatibility.

Address and data bus structure

The system board utilises all address and data lines available on the processor. This
allows up to 16 Mbytes of physical memory to be addressed.
The total addressable I/O space of the processor is 64 Kbytes. Section 5 shows how
it is used and details the I/O ports used by various devices.

Software compatibility

Existing software which has been written for the 8086/8088/80286 will be executed at
greater speed on the 80386SX/486SLC, even higher performance will be achieved with
new software which takes advantage of the 80386SX or 486SLC architecture and
enhanced instruction set.

Modes of operation

The processor enters real mode at power up or when it is reset. In this mode it provides
fast execution in an unprotected mode like that of the 8086 or 80286 in real mode. The
main difference between the 80386SX/486SLC, and the 80286/8086 in this mode is
speed.
In the protected mode the 80386SX/486SLC has all the advanced architectural features
of the 80286: memory management and protection mechanisms, task management, and
virtual memory support. In addition it operates with greater speed and supports 32-
bit registers and instructions.
In the virtual 8086 mode the 80386SX/486SLC creates one or more 8086 environments
within its protected multitask environment. This allows multiple 8086 tasks or a
mixture of 8086 and 80286/80386 tasks to be executed concurrently.
System Board
LS PRO HARDWARE TECHNICAL REFERENCE 3/5