Flash access

[chrys0720003]

Posted on November 19, 2002 at 04:49

Flash access

[chrys0720003]

Posted on September 25, 2002 at 07:14

Hello,

I would like to access an 8Mb flash on ISA bus. ISA decode A0 to A23 address line and can only access first 16Mb of address space. This 16Mb overlaps with memory. If I find a way to enable access to the flash I'm going to loose 8Mb of memory. Is there any better way to access a flash? Thanks for your help.

[vialgilles]

Posted on September 25, 2002 at 08:17

Tane,

When using the chip in local bus mode, you will be able to access full 32 bits address space and the access to the flash is going to be faster. In your case, the best is to access the flash using and address above the top of memory address. In this case, the cycle is forwarded to the PCI and if no PCI device answers, it goes to the ISA bus. The A24 to A31 lines are just ignored. I give you an example: The 0xff080000 address will go to ISA generating this address: 0x80000. You can still access your memory using 0x80000 in place of 0xff080000. The only point to watch is that you don't conflict with PCI device or STPC internal functions. I hope I answered your question, Regards, Tips

[thierry239955_st]

Posted on November 19, 2002 at 04:49

Hello Tane,

FYI: The method describe by Tips require an external decoding on ISA bus. The ROM chip select pin, usually connected to the flash, can't be used for a flash largest than 2Mb. In your case, you just have to connect the A23 line for the decoding.