2. Getting Started
18
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Local RAM Drive - 8-bit battery-backed RAM (not available on the ZT 8903) paged
for 128 Kbytes
•
System BIOS - 16-bit pseudo static RAM shadowed from Flash #0
•
Extended RAM - Optional 16-bit pseudo static RAM module
•
Flash #0 - 8-bit Flash
•
Flash #1 - Optional 8-bit Flash
•
STD bus Expansion - 8-bit or 16-bit expansion memory
•
Reserved - Not available
STD bus expansion memory is transferred at a rate of up to 1 Mbyte/second for 8-bit
data and 1.5 Mbytes/second for 16-bit data. The ZT 8904 supports the STD bus wait
request signal, WAITRQ*, to interface to memory boards with longer access time
requirements than those defined by zero wait state STD 32 specifications. During local
memory operations, the STD bus is held static to decrease system electrical noise and
power consumption.
The ZT 8904 supports 128 Kbyte battery backed RAM (BRAM) devices. BRAM is paged
into the system memory map in 64 Kbyte increments at 0xD0000h through 0xDFFFFh.
Paging is performed by writing specific values to bits D4, D3 and D2 of System Register
0 (0X7Bh). BRAM pages are selected as follows:
•
Write XXXX111Xh to select BRAM page 0
•
Write XXXX110Xh to select BRAM page 1
If larger BRAM devices are installed, use sequential codes to select subsequent pages
in the memory map. Note that specific BRAM pages are used by both the Ziatech Single
Master BIOS and by the STAR System BIOS. The Ziatech
Technical Support Group
can provide example code for using ZT 8904 BRAM.