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| 型號(hào)： | BREAKING |
| 英文描述： | Breaking through the 1 Mbyte Address Barrier Application Note? 17.3KB (PDF) |
| 中文描述： | 通過1兆字節(jié)地址屏障應(yīng)用筆記打破？ 17.3KB（PDF格式） |
| 文件頁數(shù)： | 1/3頁 |
| 文件大小： | 17K |
| 代理商： | BREAKING |
Breaking Through the 1 MByte Address Barrier
Using the Am186ES Microcontroller
The x86 architecture has come to dominate the microprocessor landscape as the most successful architecture in the
world. The 186 is the 16-bit microcontroller version of the x86 architecture and it has had similar success in the 16-bit
embedded market. New versions of the popular 186 have provided more performance, such as the Am186ES
microcontroller that provides 5.35 Dhrystone 2.1 MIPS using 70 ns memory. One area that still provides a barrier to
some applications is the 1 MByte linear address range of the 186. This is the same 1 MByte address range of the
original IBM PC. Breaking this 1 MByte address range is not as easy as setting a compiler switch, but it can be done
with a little software planning. Using the programmable I/O and the unified middle chip select capability of the Am186ES
microcontroller, this greater than 1 MByte address range can be implemented directly to the memories with no external
hardware. The SRAM interface timing, and byte write enables among other system functions are integrated into the
Am186ES microcontroller.
Consider the simple case of a typical system with Flash and SRAM that needs additional data space beyond the 1
MByte boundary. Examples of what this data may be include maps, tables of information or any data base that is
accessed in blocks, rather than randomly throughout the data base. In the case of the map, all the data associated with
a grid would be placed in one segment. A database example may be all the sales made on a certain day.
Figure 1 shows the hardware for an application requiring more than 1 MByte of memory. The upper chip select (UCS)
accesses the Am29F010 Flash containing 256 KBytes of application instructions, interrupt service routines and data that
must remain available for subroutines (for example, text strings for output). The lower chip select (LCS) accesses to
provide the interrupt vector table, stack space and any other volatile memory requirements. The middle chip select 0
(MCS0) connects to the additional Am29F016 Flash memory and is set for 256 KBytes. The unified middle chip select
capability of the Am186ES means that larger sections of memory can be accessed through the single chip select. The
programmable IO (PIO) act as additional address bits into the Am29F016 Flash memory. In this configuration, there are
256 KBytes of SRAM, 256 KBytes of Flash in the Am29F010 always available, 256 KBytes of address space for other
system requirements and 16 independent Flash segments of 256 KBytes each in the Am29F016 Flash. The total
memory, SRAM and Flash, available is 4.5 MBytes. Obviously, there is still a great deal of flexibility remaining in the
address map to adapt this to a particular embedded application’s requirements. Larger or smaller memories could be
used as needed.
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