Theory of Operation
Setting the Map Register
Follow these steps to load the Map Register:
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.
Put the upper four bits of the Map Register index number into
the Map High Address Register. This register must be set to
0000 for 20-bit address systems and need not be changed once
initially loaded (see page 3-20 for 24-bit addressing).
5.
Put the lower six bits of the Map Register index number into the
Map Low Address Register. Typically, the lowest index number
will be entered and will then be incremented by software for
each successive Map Register number.
6.
Write the data to the Map Register (bit 8 = logical 1 to enable
the Map Register, bits 7-0 = page number).
7.
When all 64 (or 1,024) Map Registers have been loaded, reset
the Configuration Register Map Write Enable bit (bit 2) to
logical 0 to protect the registers from further changes.
8.
Disable Absolute Addressing by setting Configuration Register
bit 1 to logical 1.
9.
Set the Configuration Register Alternate Map Register bit (bit 7)
to:
a)
logical 0 to access the Primary Map Register set.
b)
logical 1 to access the Alternate Map Register set.
3-18
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