
2-2
Memory Management
2.1
SYSTEM MEMORY: DRAM AND BUS
Figure 2-1 on page 2-2 shows a typical system address space for the élanSC310 micro-
controller.
The three regions of system-address space are conventional memory (the first
640 Kbyte), high memory (the next 384 Kbyte), and extended memory (the remaining
15 Mbyte). Only the first Mbyte (conventional and high memory)—along with the first
64 Kbyte of extended memory—can be accessed while the élanSC310 microcontroller is
in Real mode without using the MMS. All 16 Mbyte of system-address space may be
addressed while the élanSC310 microcontroller is in Protected mode. For more informa-
tion on Real and Protected modes, see the
Am486
Manual
, PID 18497.
Microprocessor Software User’s
In Figure 2-1 on page 2-2, the shaded portion of the address space represents on-board
memory. That is, it represents the portion of the system address space that is currently
associated with physical memory chips attached to the élanSC310 microcontroller’s sys-
tem board (e.g., in SIMMs). The unshaded portion can be associated with memory
devices connected to the ISA or local bus. These addresses will be empty if no ISA or
local-bus memory devices are attached.
For on-board memory, the élanSC310 microcontroller supports only DRAM.
The élanSC310 microcontroller supports two different bus configurations:
I
Local bus with a partial ISA bus
I
Maximum ISA bus
The selection of one of these two options must be made when the system is designed
and may not be changed dynamically. This choice also affects the meaning and behavior
of several pins. For information on exactly which pins are affected, refer to the
Microcontroller Data Sheet, PID 20668
.
élanSC310
Figure 2-1
Typical AT Address Space
000000h
Extended
Memory
0A0000h
09FFFFh
0FFFFFh
100000h
FFFFFFh
Top of on-board memory
640 Kbyte
1 Mbyte
16 Mbyte
High
Memory
Conventional
Memory