Don't you have to set the processor in protected mode to access the
extended memory? Not available by direct addressing in real mode.

Here is a book that has some stuff that may be useful.

PC Architecture and Assembler Language
by Barry Kauler
ISBN 0-646-03348-4

In Australia it's from Karda Prints in Edgewater, WA and in the USA from
Annabooks in San Diego, CA.

Good luck,
Bill

At 02:14 PM 6/01/98 EST, you wrote:
>        Totally off topic, but I figure there are some experts here that
>I have not found on pc newsgroups.
>        I'm working with Data Light's ROM-DOS, putting a BIOS extension
>at 0 d000:0 that refers to data at 8 0000:0.  My hardware seems to be
>working with the stuff in conventional memory, but neither view-xm nor
>rom-dos can find the stuff in extended memory.
>        In a PAL (16R8), I'm generating chip selects to drive the EPROM
>and a 74hc245 bus transceiver based on latching LA23..LA20 and A19..A16
>on the negative edge of ALE.  For the chip enable to go true, AEN also
>has to be low (not in a DMA cycle).
>        Anyone have more experience with the ISA bus?  I've got a logic
>analyzer coming in this morning to dig into it.  One question that
>remains to me, however, is how does the motherboard memory map decoding
>know where to go to find memory?  Stuff in extended memory COULD be in
>SIMMS, or could be on the ISA bus.  Does it go looking during POST and
>map stuff accordingly?
>
>THANKS!
>
>Harold
>