Theory of Operation
EXTENDED MEMORY MODE
The ZT 8825 can be used as normal memory anywhere in the
16 Mbyte address space by using 24-bit addressing. Memory is
mapped in 16 Kbyte blocks, allowing it to be distributed over
16 Mbytes of address space.
Setting the 24-bit Map Register
To set the Map Register for 24-bit addressing, after installing Jumpers
W2-W5:
1.
Disable the board by setting the Configuration Register Map
Enable bit (bit 0) to logical 0.
2.
Set the Configuration Register Map Write Enable bit (bit 2) to
logical 1.
3.
Set the Configuration Register Alternate Map bit (bit 7) to:
a)
logical 0 to load the primary Map Register set.
b)
logical 1 to load the Alternate Map Register set.
4.
Set the Map High Register to 0000.
5.
Set the Map Low Register to 000000.
6.
Allow software to increment the Map Low Register index
number by one for each successive Map Register number until
the Map Low Register has been filled (64 increments).
7.
Allow software to increment the Map High Register by one and
then reset the Map Low Register to 000000.
8.
Repeat steps 6 and 7 until both low and high registers have filled
(16 times).
9.
When all 1,024 Map Registers have been loaded, reset the
Configuration Register Map Write Enable bit (bit 2) to logical 0
to protect the map data.
3-20
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