Acer 486 Manuel d'utilisateur télécharger pdf (Page 37)

Am486

Microprocessor PCI Customer Development Platform

2-7

Board Restrictions

• Using a PCI chipset with the Am486 microprocessor is a fast and effective way

to design a working system, but the system’s features can be limited by the

chipset’s capabilities.

• The chipset used in the PCI CDP supports 5-V PCI 2.0 devices only. Three

devices are supported: the onboard Ethernet controller and two PCI slots.

• Except for the adjustable CPU supply voltage and 3.3-V Ethernet controller, the

PCI CDP uses 5-V power throughout. (The Am486 microprocessor provides 5-

V-tolerant I/O.)

• The chipset does not directly support ROM or Flash memory devices except for

the boot ROM. It is possible to implement Flash memory on the DRAM, PCI

or ISA bus, but the chipset only allows booting from the boot ROM. ISA-bus

Flash memory is limited to 1 Mbyte because of addressing considerations.

• The PCI CDP implements two banks of execute-in-place (EIP) Flash memory

in place of one DRAM bank. Flash memory timing requirements limit the

chipset’s DRAM interface to its Fast (not Fastest) speed when the Flash memory

is used. This is equivalent to using 70-ns fast-page-mode (FPM) DRAM.

• The chipset allows only three banks of DRAM to be attached without external

buffers. Buffering the DRAM adds one wait state and reduces the available

performance. “DRAM Main Memory (P7)” on page 2-20 describes additional

DRAM device and configuration limits.

• The ISA peripherals provided by the M1487 chip are configured for standard

PC-AT compatibility, so there is not much flexibility in assigning interrupts and

DMA channels.

• The PCI CDP does not implement OnNow or Advanced Configuration and

Power Interface (ACPI) power management.

Board Features

The remainder of this chapter describes the features of the PCI CDP. The number

in parentheses following each heading indicates the part’s location in Figure 2-3

on page 2-5. In addition, other locations referenced can be found in the figure.

1 2 ... 32 33 34 35 36 37 38 39 40 41 42 ... 109 110

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Acer 486 Manuel d'utilisateur Page 37