Theory of Operation
MEMORY ADDRESSING
The ZT 8825 is designed to operate with the STD-80 Series
multiplexed memory address scheme. Therefore, while address bits
A0-A15 have their own dedicated backplane pins, A16-A23 are
multiplexed onto the data bus pins during T1 of a memory access.
The MCSYNC* (machine cycle sync) signal is used to latch the
addresses on the ZT 8825. The MEMEX (memory expansion) signal
is not used by the ZT 8825.
20-bit Memory Addressing
The default memory addressing configuration (Jumpers W2-W5 out)
is for 20-bit addressing. On-board pull-down resistors on the internal
addressing lines A20-A23 make the Map Registers believe that these
upper four address bits are zeros. That is, the 1 Mbyte address space
is at the bottom of the 16 Mbyte Extended Memory address space. 20-
bit addressing allows for 64 Map Registers (see page 3-15 for more
information on Map Registers).
24-bit Memory Addressing
Even though the ZT 8825 was designed to work explicitly with the
multiplexed 20-bit memory address scheme of the STD-80 Series Bus
Specification, it will work with a 24-bit address STD bus (for
example, 80286 or similar processors). 24-bit addressing allows for
1,024 Map Registers or 16 Mbytes of address space.
Memory
between 1 Mbyte and 16 Mbytes is known as Extended Memory.
Install Jumpers W2-5 to configure the ZT 8825 for 24 bit addressing.
For more information on configuring your board for memory
addressing, refer to page 5-12.
3-13
Artisan Technology Group - Quality Instrumentation ... Guaranteed | (888) 88-SOURCE | www.artisantg.com