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On Thu, 10 Feb 2000, Stefan Reinauer wrote:
Is there a secure way to access anything in the CMOS over 128 bytes? I wrote some patches for the Linux nvram driver a long time ago to access not only ,64 bytes, but 128 bytes. I read somewhere that everything over 128 bytes has to be accessed over io registers 0x72 and 0x73 instead of 0x70 and 0x71. Has anyone information on that issue?
You need to check datasheets of particular chips (for example look at Dallas Semiconductor's site for specs of DS12887) to see how to access the extra space (IIRC, DS12887 uses banking). For PC machines, bit #7 at 0x70 is used to drive an external NMI mask latch.