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Acer A1 Motherboard

Jumper and Connector Layout

a1 board diagram

Note - The blackened pin of a jumper represents pin 1.

Overview

The following lists the major features of the Acer A1 system:

  • 486SX, DX or DX2-series CPU
  • 4-MB on-board RAM expandable to 36-MB
  • two 72-pin SIMM sockets for memory upgrade
  • 120-pin connector for ISA raiser card
  • 128-KB ROM for system BIOS and VGA BIOS
  • optional on-board cache memory (64-KB, 128-KB or 256-KB)
  • system clock/calendar
  • two 9-pin serial ports
  • one 25-pin Centronics parallel port
  • 512-KB or 1-MB DRAM for ultra-VGA interface, expandable to 1 or 2 MB
  • embedded hard disk interface
  • One PS/2-compatible keyboard port
  • One PS/2-compatible mouse port

Jumper Settings

JumperSettingFunction
JP1OPENACER BIOS
 CLOSEDOEM BIOS
JP21-2Enable Password (Security)
 2-3Disable Password (Security)
JP41-2Flash ROM
 2-3EPROM
JP51-2Normal Floppy
 2-33Mode Floppy
*JP71-233MHz
 2-325MHz
*CN143-733MHz (DX2/66)
 4-825MHz (DX2/50)
* You need to set only one jumper, either CN14 or JP7 to select the CPU clock speed.
JP14CLOSEEnable On-Board VGA
 OPENDisable On-Board VGA
JP19CLOSEDebug Jumper (Always Closed)
JP22OPENLock Key
 CLOSEDUnlock key
JP281-2Enable On-Board Memory
 2-3Disable On-Board Memory or No On-Board Memory

System CPU Clock Selection

CPU ClockJP7JP8JP9JP10JP17
25MHz (DX2/50)2-32-31-22-32-3
33MHz (DX2/66)1-22-31-22-32-3
40MHz1-21-22-31-21-2
50MHz2-32-31-21-21-2

CPU Type Selection

CPU TypeJP11JP12JP13JP15JP18JP20JP27
4861-21-21-21-22-32-3OPEN

Memory

The system board has two SIMM sockets that accept 4-MB, 8-MB, or 16-MB SIMMs, upto a maximum of 32MB (or 36MB if motherboard has 4MB on-board). 72 Pin, 70ns, Parity, Fast Page Mode SIMMS with gold tips recommended.


Cache RAM Upgrade Path

Cache SizeSRAM TypeLocationJP24JP25JP26
64KB8K X 8 X 9 PCSTAG, U56 TO U63OPENOPEN2-3
128KB32K X 8 X 5 PCSTAG, U56,U58,U60,U62OPENCLOSED1-2
256KB32K X 8 X 9 PCSTAG, U56 TO U63CLOSEDCLOSED2-3

Upgrade Video Memory

You can increase VGA RAM to 1 or 2 MB.

To upgrade the VGA RAM, do the following:

1. To upgrade from 512 to 1MB, order p/n 91.00023.901 from Acer Access. To upgrade from 1MB to 2MB order p/n 02.54260.030.
2. Locate the VGA memory expansion sockets on the system board labelled U12, U13, U15 and U16.
3. Gently but firmly insert a 44256 DRAM (256 K bit by 4, 70-ns) chip into each of the VGA memory expansion sockets.

Increasing VGA memory up to 2 MB is an option available to you. To do this, insert two 51460 (256 K bit by 16) DRAM chips on the sockets labelled U10 and U9.