Page 286 - Embedded Microprocessor Systems Real World Design

CompactPC/

A drawback to the standard ISA bus in a PC (and the similar PC/104 bus) is speed.
ISA is limited to 16-bit transfers and, for compatibility reasons, limited in speed.
The PCI bus in a PC overcomes some of these limitations with a high-speed bus
that supports 64bit transfers and has a more flexible interrupt structure. The
origmal 33MHz PCI bus supports burst transfer rates of 133MB/sec using a 32-bit
mode, and 266MB/sec using a 64bit mode. However, the PCI bus, as implemented
in a PC, still has drawbacks for industrial applications since it uses edge connectors
and a single-screw holddown mechanism similar to the ISA.
The CompactPCI adapts the PCI bus to industrial and embedded applications.
Like VME cards, CompactPCI boards are based on the Eurocard industry standard.
CompactPCI boards come in 3U and 6U sizes. The connector is a 5 row x 44 pin
connector, with 2mm pin-to-pin spacing. The cards are held in place by a rail
attached to the card-cage frame at each end with screws for secure mounting.

CPU on a Chip
The AMD Elan SC520 Microcontroller provides a 32-bit, 100MHz, 586 CPU core
with several integrated peripherals. These include:
e Integrated PCI host bridge
0 SDRAM controller
e Programmable interrupt controller
0 PGcompatible timer
0 PGcompatible DMA controller
e Two 16550compatible UARTs
e Real-time clock with battery backup
e Three general-purpose timers
0 Watchdog timer
e Synchronous serial interface
e Programmable address decoding (chip selects)
e 32 general-purpose 1/0 pins
The Elan SC520 is optimized for embedded applications and provides a highly
integrated solution when a PGcompatible embedded controller is needed.

Example Real Time PC Application

When the original IBM PC was introduced, it was not well suited to embedded real-
time control. With CPU clock rates of 5 or 12MHz and unpredictable operating
system performance, you just couldn’t be sure things would be done in a timely

Industry-Standard Embedded Platfolms 267