Bios Rom; Cmos Ram; Video Dram - Epson NX Service Manual

Subassembly Descriptions
Shadow RAM
128KB of the remaining first 1MB of DRAM is used to shadow the system BIOS and VGA
BIOS. Shadow RAM is address selectable through SETUP.
Cache Memory
8KB of internal cache is built into the microprocessor. Cache address control is selectable
through SETUP and testing is available through the system diagnostics.
The system also supports a new feature designed by Epson called VirtualCache. VitualCache
is a dynamic DRAM memory cache that functions like cache SRAM. VirtualCache utilizes
the burst-mode capabilities of the 486 CPU to minimize memory access time. In addition,
look-ahead circuitry attempts to predict where the next memory access will be, and access
that region before the CPU needs it.

BIOS ROM

The system uses a BIOS that conforms to the ISA IEEE specifications. The BIOS supports
all applications that run on PC XT/AT systems and supports all ISA option cards.
The system board contains a 128KB EPROM in Ul for the system and video BIOS plus the
code for the SETUP utility. The 64KB EPROM in U113 contains the Nanguage text
messages for SETUP
The current BIOS version is shown during system start up. Installing a new version of the
BIOS requires replacement of the EPROMs in Ul and U113. See Chapter 3 for details.

CMOS RAM

The CMOS RAM is contained within the 82C206 and power is provided via the lithium
backup battery. The CMOS memory supports the standard 64 bytes of battery-backed RAM:
14 bytes for clock and control registers and 50 bytes of general purpose data. All CMOS
RAM is reserved for BIOS use and can be set to specific values or cleared to system default
values using the SETUP program.

Video DRAM

The system comes with 2MB of video DRAM consisting of eight 256KB chips soldered onto
the main system board in sockets U84-U87 and U92-U95.
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