Acer 486 User manual

& K DSWHU

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System Board

System Board 1-1

This high-performance, 32-bit personal computer system is based on

the 486 series microprocessor. It features the single-chip upgrade

technology which allows maximum ease and flexibility for upgrading

the system. It is fully compatible with the IBM PC/AT and is suitable

for use as a Windows workstation, CAD/CAE/CAM workstation, UNIX

personal workstation or desktop PC.

The system board accommodates an ISA riser card slot and two 72-

pin SIMM sockets that can hold a maximum memory of 36 MB. The

system architecture is based on the VESA local bus featuring an

onboard VGA. The VGA memory is expandable to 1 MB or 2 MB.

In a LAN environment, the system supports 16-bit Arcnet cards,

Ethernet cards and Token Ring cards. It is fully compatible with Novell

NetWare and Microsoft LAN Manager and also with SCO UNIX,

XENIX and OS/2 operating systems.

The system has a number of software-controlled security features.

These include power-on password, disk drive read/write control,

diskette boot control, serial- and parallel-port control, and a system

setup control.

Installing options such as memory modules, expansion boards and an

upgrade CPU enhance system performance. This chapter gives step-

by-step instructions on how to install these options.

1-2 User’s Guide

1.1 System Board Layout

The system board has the following major components:

•486SX, SX2, DX2, or DX4 series CPU

•4-MB onboard RAM expandable to 36 MB

•Two 72-pin SIMM sockets for memory upgrade

•128-KB ROM for system BIOS and VGA BIOS

•120-pin connector for ISA riser card

•System clock/calendar

•Two 9-pin serial ports

•One 25-pin Centronics parallel port

•PS/2-compatible keyboard and mouse interface

•512-KB or 1-MB DRAM for onboard local bus VGA interface;

expandable to 1 MB (for GD-5424) or 2 MB (for GD5429)

•Embedded fixed disk interface

•Upgradable cache memory (128-KB or 256-KB)

•Optional enhanced IDE interface

•Optional power daughter board that enables the system to

support the 3.3V microprocessors

Figure 1-1 shows the board layout and the locations of the important

components.

System Board 1-3

1. Keyboard controller 17. Power daughter board

2. M5105 super I/O controller 18. M1429G system chip

3. System and VGA BIOS 19. Onboard memory (4 MB)

4. RTC Battery 20. SIMM sockets

5. Power connector 21. VGA feature connector

6. IDE fixed disk connector #2* 22. VGA connector

7. IDE fixed disk connector #1 23. Parallel port

8. Diskette drive connector 24. COM2 port

9. ISA riser card connector 25. COM1 port

10. Local bus IDE controller* 26. PS/2 mouse connector

11. M1431 system chip 27. PS/2 keyboard connector

12. Second-level cache* 28. VGA upgrade sockets (1 MB)

13. Power daughter board connectors 29. VGA upgrade sockets (2 MB)

14. TAG RAM 30. Onboard VGA memory (512 KB)

15. Fan power connector 31. VGA chip

16. 486 CPU socket

Figure 1-1 System Board Layout

*Optional

1-4 User’s Guide

1.2 ESD Precautions

Electrostatic discharge (ESD) can damage your processor, disk drives,

expansion boards, and other components. Always observe the

following precautions before you install a system component.

1. Do not remove a component from its protective packaging until

you are ready to install it.

2. Wear a wrist grounding strap and attach it to a metal part of the

system unit before handling components. If a wrist strap is not

available, maintain contact with the system unit throughout any

procedure requiring ESD protection.

Integrated circuits are extremely susceptible

to electrostatic discharge. Do not handle ICs

unless you are a qualified service technician,

using tools and techniques that conform to

accepted industry practices.

1.3 Pre-installation Instructions

Follow these steps before you install a system component:

1. Turn off the system power and all the peripheral devices

connected to the unit before you open it.

2. Open the system according to the instructions in the housing

installation manual.

3. Follow the ESD precautions in section 1.2 before handling a

system component.

4. Remove any expansion boards or peripherals that block access

to the SIMM sockets or CPU socket.

5. See the following sections for specific instructions on the

component that you wish to install.

System Board 1-5

Do not attempt the procedures described in

the following sections unless you are a

qualified service technician.

1.4 Jumper Settings

Figure 1-2 shows the jumper locations.

Figure 1-2 Jumper Locations

1-6 User’s Guide

The following tables list the jumper settings and their correponding

functions.

Table 1-1 System Board Jumpers

Jumper Setting Function

JP2 1-2

2-3 Enable password check

Bypass password

JP14 Closed

Open Enable onboard VGA

Disable onboard VGA

JP16 Open

Closed Enable onboard local bus IDE

Disable onboard local bus IDE

JP21 Closed

Open Enable onboard super I/O chip

Disable onboard syper I/O chip

JP28 1-2

2-3 Enable onboard memory

Disable onboard memory

JP37-38 1-2

2-3 Enable Reset button

Enable Suspend/Resume button

Table 1-2 CPU Clock Selection

JP10 JP17 JP19 CN14 CPU Clock

2-3 2-3 2-3 3-7 33 MHz (for SX/33,

DX2/66 or DX4/100)

2-3 2-3 2-3 4-8 25 MHz (for SX2/50

or DX2/50)

System Board 1-7

Table 1-3 CPU Type Selection

4861486 WB2Pentium

OverDrive AMD

486/DX2 AMD

486/DX4 Cyrix

IBM TI

JP11 1-2 1-2 1-2 1-2 1-2 2-3 2-3

JP12 1-2 2-3 2-3 1-2 1-2 1-2 2-3

JP13 1-2 1-2 1-2 1-2 1-2 1-2 2-3

JP18 2-3 1-2 1-2 2-3 2-3 2-3 2-3

JP20 2-3 2-3 2-3 2-3 2-3 1-2 2-3

JP30-32 Open Open Open Open Open Closed Open

JP33 1-2 1-2 1-2 1-2 1-2 2-3 1-2

JP34-36 Closed Closed Closed Open Open Open Open

JP39 1-2, 4-5 1-2, 4-5 1-2, 4-5 1-2, 4-5 1-2, 4-5 1-2, 4-5 2-3, 5-6

JP40-41 2-3 2-3 2-3 1-2 1-2 2-3 2-3

JP42 2-3 2-3 2-3 2-3 2-3 2-3 1-2

JP43 Open Open Open Open Open Open Open

JP46 1-2 2-3 2-3 1-2 1-2 1-2 1-2

JP47 1-2 1-2 1-2 1-2 1-2 2-3 1-2

JP48 Open Open Open Closed Open Open Open

Table 1-4 Cache RAM Size Selection

JP24 JP25 JP26 Cache Size

Open Closed 1-2 128 KB

Closed Closed 2-3 256 KB

1Intel 486SX, SX2, DX, DX2 and DX4

2Intel 486DX2 and DX4 with write-back internal cache

1-8 User’s Guide

1.5 Installing Memory

The system board has two 72-pin SIMM sockets that accept 1-MB, 2-

MB, 4-MB, 8-MB, or 16-MB memory modules with 80 ns (or less)

DRAM speed. The maximum system memory size is 36 MB.

When installing additional memory, choose one of the SIMM

configurations listed in Table 1-5.

Table 1-5 Memory Configurations

Onboard Socket 1 Socket 2 Total

4 MB 4 MB

4 MB 1 MB 5 MB

4 MB 1 MB 1 MB 6 MB

4 MB 1 MB 2 MB 7 MB

4 MB 4 MB 8 MB

4 MB 4 MB 1 MB 9 MB

4 MB 4 MB 2 MB 10 MB

4 MB 4 MB 4 MB 12 MB

4 MB 4 MB 8 MB 16 MB

4 MB 16 MB 20 MB

4 MB 16 MB 1 MB 21 MB

4 MB 16 MB 2 MB 22 MB

4 MB 16 MB 4 MB 24 MB

4 MB 16 MB 8 MB 28 MB

4 MB 16 MB 16 MB 36 MB

System Board 1-9

1.5.1 Installing a SIMM

Observe ESD precautions when installing

SIMMs. See section 1.2.

Follow these steps to install a SIMM:

1. Insert the SIMM into the socket at a slight angle, making sure that

the cut edge of the SIMM touches the base of the circle mark on

the SIMM socket.

2. Gently press the SIMM back against the holding clips on both

ends of the socket until the peg slips into the holes on the SIMM,

and the holding clips lock the SIMM into position. See Figure 1-3.

3. Check that the SIMM is securely seated in its slot and that both

ends are locked to the socket.

Figure 1-3 Installing a SIMM

1-10 User’s Guide

1.5.2 Removing a SIMM

Observe ESD precautions when removing

SIMMs. See section 1.2.

1. Press the holding clips on both sides of the SIMM outward to

release it.

2. Push the SIMM upward.

3. Gently pull the SIMM out of the socket.

Figure 1-4 Removing a SIMM

1.5.3 Reconfiguring the System

The system automatically detects the amount of memory installed.

Run Setup to view the new value for total system memory and make a

note of it.

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