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Chapter 6 Controller Board
DRAM
System DRAM is used for program variables, image buffers, and input
buffers. All DRAM supports page mode operation and is addressable by
individual byte.
Two standard 72-pin DRAM SIMMs are used for expansion memory. The DC,
through the VX ASIC, may address up to 32MB of DRAM in four banks.
NVRAM
An 8K x 8 bit Non-Volatile battery-backed static RAM (NVRAM) device
provides for the storage of configuration and system statistical data.
VX ASIC
The VX is a multi-function custom gate array ASIC containing all the logic for
the DC that is not contained in the 68EC030 processor. The VX provides the
following services:
• Memory Access Controller
• DRAM Controller
• Flash Controller
• Two DMA Channels
• Operator Panel Interface
• “Dot Plucking” and Adjacent Dot Checking
• “Cajun” Bus Interface
• Host I/O and Diagnostic Port
Memory Access Controller
All 030 addresses go through the VX ASIC. The VX handles all address
decoding, chip selects, DTACKs, and so on.
DRAM Controller
The VX supports up to four banks of page mode DRAM.
Flash Controller
The VX supports up to four banks of flash memory.
DMA Channels
The VX provides two channels for direct memory access. These channels
move data from the host interface or expansion bus to the DRAM and vice
versa. One address is an I/O address, the other is a memory address with
auto-increment.
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