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Theory of Operation
Replacing the battery is a simple task. However, removing the battery will invalidate
the CMOS setup parameters. It is recommended that all setup parameters be written
down while the battery is still good.
Video Controllers
3
3
The EPC can operate with or without a video controller such as the EXM-13A.
At power-up, the BIOS searches the EXM configuration information by slot number
(starting at 0) for the first video EXM where the card enable bit is set. If one is
found, it will be initialized and used at power-up and the search exits.
If no video card is enabled in the EXM configuration information, a second search is
done across the EXM expansion interface (beginning at slot 0) looking for an EXM
video adapter. When a video adapter is found, the system will enable it and quit the
search.
If no EXM video adapter is found, the BIOS looks for any card with video BIOS.
The CPU scans the memory space from A0000h to C8000h looking for any memory
location containing the value AA55h. If such memory is found (video BIOS ROM),
the main BIOS performs a "jump" into the video card BIOS and executes whatever
code is found allowing that card to be used.
If no video controller is present, the BIOS operates without one. Programs that use
the standard operating system and BIOS character output functions run successfully
because the output is ignored. However, programs that rely on specific video modes,
that write directly into the video RAM, or that directly call video BIOS functions,
will fail.
Front Panel LED
The EPC-23 has one LED on the front panel. This RUN LED is lit whenever the
EPC's memory is being accessed. It first comes on at power-up and should remain lit
as long as the system is running. It is normal for the RUN LED to flicker during
power-up. If the processor halts (or hangs), the LED will go out.
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