Theory of Operation
10.
Normally, the Configuration Register RAM Write Enable bit (bit
3) will be set to logical 0 at this time.
11.
Enable the board by setting the Configuration Register Map
Enable bit (bit 0) to logical 1.
Absolute Address Mode
For ease of start-up in simple systems, the ZT 8825 can be configured
to come up at power-on or reset time in an "absolute address mode."
To enable absolute address mode:
1.
Install Jumper W1.
2.
Set Configuration Register bit 1 to logical 0.
3.
Set Configuration Register bit 3 to logical 1.
The board behaves in this mode as though its memory is a linear
block starting at address 0 and continuing to the upper limit of
memory on the board.
This is useful for small systems where the ZT 8825 is the only RAM
board or in systems where it is used for RAM disks and for lower
memory. Only one ZT 8825 in a system can use absolute address
mode.
The ZT 8825 cannot be used in absolute address mode in DOS
systems because the ZT 8825 powers up with its RAM write
protected.
Non-DOS systems with boot ROMs can disable ZT 8825 write
protection while executing custom code. To do this, the ROM code
must output 08h to I/O location base+3 (default EE68h).
Absolute address mode can be turned off in software by setting the
Configuration Register bit 1 to logical 1 after programming the Map
Registers as described above. It may be permanently disabled by
removing Jumper W1.
3-19
Artisan Technology Group - Quality Instrumentation ... Guaranteed | (888) 88-SOURCE | www.artisantg.com