Specifications

Theory of Operation
4 4
4-1
Chapter 4 - Theory of
Operation
Overview
The EPC-8 is a PC/AT compatible computer with standard PC peripherals, a VMEbus
interface, and modular expansion capability via the EXM expansion interface. Figure
4-1 provides an diagrammatic overview of the system functional blocks. Most of the
standard functions of the PC architecture are embodied in the VLSI 82C486 chipset.
DRAM and VGA are interfaced to the 486 processor by a 32-bit local bus. The
customary PC peripheral interfaces for keyboard, two serial ports, a parallel port, and
a battery-backed real-time clock are connected by the EXM expansion interface which
is electrically similar to the standard PC ISA bus. An Ethernet controller is built onto
the EPC-8 board.
The VMEbus interface includes special VME byte swapping hardware to aid the
software when dealing with different processor and memory organization. This is
described in detail later in this chapter.
The EPC-8 maps a standard set of VXI configuration registers onto the VMEbus A16
space. These are dual-ported and accessible both by other VMEbus modules and the
EPC-8 in its I/O space.
Resident Flash memory (on the EPC-8 board) is I/O mapped and appears as an EXM
expansion module as if in EXM slot 31. SRAM is memory mapped. The PC BIOS is
shadowed into main memory at start-up.
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