Theory of Operation
Configuration Register
The Configuration Register allows software control of several board
parameters associated with memory mapping. Figure 3-4 illustrates
the Configuration Register bits that affect these parameters. The fol-
lowing is a description of the purpose of each Configuration Register
bit:
Bit 0
Map Enable bit. Setting bit 0 to logical 1 turns on the
board’s mapping functions. Bit 0 must be set to logical 0
when changing the Map Registers.
Bit 1
Absolute Address Disable bit.
Use Bit 1 to choose
between an "absolute address mode" (see page 3-19) and
addressing modes using the mapping function. Set bit 1
to logical 0 to select absolute address mode.
Bit 2
Map Write Enable bit. Set bit 2 to logical 0 to protect the
Map Register data from being overwritten. Bit 2 must be
set to logical 1 to load the Map Registers.
Bit 3
RAM Write Enable bit.
Use bit 3 to control write
protection of RAM (see page 3-6) in software. Set bit 3
to logical 0 to protect RAM from being altered.
Bits 4 - 6
Undefined.
Bit 7
Alternate Map Register Enable bit. Set bit 7 to logical 1
to enable access to a complete alternate set of Map
Registers.
1
2
3
4
5
6
7
0
Alternate
Map
Register
Enable
bit
Map
Write
Enable
bit
Absolute
Address
Disable
bit
Map
Enable
bit
RAM
Write
Enable
bit
Figure 3–4. Configuration Register.
3-17
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