This document is for the baby-sized (13.3" x 8.5") Baby Gemini 486SX-25 motherboard.
It is also known as the "Upgradeable" board because it can accommodate the Intel
OverDrive CPU. The part number for this board is 09-00145-xx.
It's identifying features are: an LED between expansion slots #5 and #6; eight 16-bit
expansion slots; four sockets for SIMMs (using 72-pin SIMMs); one proprietary 80-pin
SIMM socket which accommodates a Micronics External Cache Card.
The bus speed for this motherboard is fixed at 8MHz.
+=============================+
+ MOTHERBOARD SWITCH SETTINGS +
+ +
+ * = Default setting +
+=============================+
SW1
---
1 Memory size (see below)
2 Memory size (see below)
3 Memory size (see below)
4 Memory size (see below)
5 Reserved *Off
6 Reserved *Off
7 Reserved *Off
8 Reserved *On
DIP switch settings for memory size
===================================
Memory Banks DIP Switch 2
-----------------------------------------------
MB 0 1 2 3 S1 S2 S3 S4
---- ---- ---- ---- ---- ---- ---- ---- ----
4MB 4M ON ON ON ON
8MB 4M 4M OFF ON ON ON
12MB 4M 4M 4M ON OFF ON ON
16MB 4M 4M 4M 4M OFF OFF ON ON
16MB 16M ON ON OFF ON
20MB 4M 16M ON ON OFF OFF
24MB 4M 4M 16M ON OFF ON OFF
28MB 4M 4M 4M 16M OFF ON ON OFF
32MB 16M 16M OFF ON OFF ON
36MB 4M 16M 16M ON OFF OFF OFF
40MB 4M 4M 16M 16M OFF OFF ON OFF
48MB 16M 16M 16M ON OFF OFF ON
52MB 4M 16M 16M 16M OFF OFF OFF OFF
64MB 16M 16M 16M 16M OFF OFF OFF ON
In the table above, 4M indicates that one 1Mx36 SIMM is installed in the socket,
16M indicates that one 4Mx36 SIMM is installed in the socket. The above shows all
of the possible memory configurations.
When installing more than 16MB of memory, BIOS relocation must be disabled. Bios
relocation copies the video Bios (C0000-C7FFF) and the system ROM Bios (F0000-FFFFF) into
RAM. The motherboard adds 15MB to these addresses (F00000) to be able to differentiate
between the ROM and RAM. Enabling the relocation feature causes the memory above 16MB
to become non-contiguous and therefore inaccessible.
Micronics Computers has tested and verified the following 1Mx36 memory brands:
Micron Technologies, Mitsubishi, Samsung, Texas Instruments, Toshiba
Micronics Computers has tested and verified the following 4Mx36 memory brands:
Mitsubishi, Samsung, Toshiba
+=============================+
+ MOTHERBOARD JUMPER SETTINGS +
+=============================+
J5 External 6-volt battery connector
Pin 1 - Battery Positive
Pin 2 - no connector
Pin 3 - Ground
Pin 4 - Ground
J7 Keylock / Power LED
Pin 1 - Power LED signal
Pin 2 - no connector
Pin 3 - Ground
Pin 4 - Keyboard lock signal
Pin 5 - Ground
J8 External speaker
Pin 1 - Speaker
Pin 2 - no connector
Pin 3 - Ground
Pin 4 - +5 volts DC
W1 Turbo LED
Pin 1 - Signal
Pin 2 - Ground
W2 Reset switch
Pin 1 - Signal
Pin 2 - Ground
W3 Turbo switch
Pin 1 - Signal
Pin 2 - Ground