Specifications

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Chapter 4
Theory of Operation
Overview
The EPC-8A is a PC/AT compatible computer with standard PC peripherals, a VMEbus
interface, and modular expansion capability via the EXM expansion interface. The Block
Diagram on page 30 provides an diagrammatic overview of the system functional blocks.
Most of the standard functions of the PC architecture are embodied in the RadiSys
R400EX chipset. DRAM and VGA are interfaced to the 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-8A 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-8A 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-8A in its I/O space.
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