Bull Micral 500

Made in France

rf7080a.exe Model 70/80 386 Reference Disk v1.12 (zipped image)
   Warning: The original Micral 500 refdisk is pure unobtainium. Use the PS/2 Model 70/80 refdisk to configure the system. It's not perfect (base memory not being reported correctly) but it works.

Paradise/WD VGA files (Metropoli BBS files, archived)

Micral 500 Planar
System Firmware
   ROM Images
Exhaust Fan Assembly
Speaker/Battery/LED Assembly
   Interconnect Board
   LED Board
   Battery Pack
Power Supply

Photos, ROM images, and other material provided by Stefan Lemanski.

Specifications (Type CPU1334) [P] [P]

CPU: i80386DX 20 MHz (PGA), optional math co-pro (PGA)
Memory: 8x 30-pin SIMM slot on the planar (industry standard?)
Bus: MCA, 1x 32-bit, 3x 16-bit (one w/ AVE, one internal)
Video: Paradise VGA (on-board), 256 KB video RAM
HDD: WD1007V-MC1 ESDI + Seagate ST1201E (200 MB)
FDD: 3.5" 1.44 MB (34-pin, Mitsubishi MF355C-213U)
I/O: PS/2 keyboard & mouse, 1x 25-pin serial, 1x parallel

The machine imitates the original PS/2 Model 80 with the 16 MHz Type 1 planar (ID FEFF, model F8, submodel 0).

Micral 500 Planar N290619000-08K, A-M-020078 [P] [P]

F1 125 V / 3 A LF Fuse (PS/2?)
OSC1 48.0000 MHz osc
OSC2 40.0000 MHz osc
OSC3 14.3181 MHz osc
OSC4 36.0000 MHz osc (PVGA mem.)
OSC5 28.3220 MHz osc (PVGA video)
OSC6 25.1750 MHz osc (PVGA video)
P1,2 16-bit MCA slot
P3 32-bit MCA slot
P4 16-bit MCA slot w/ AVE
P5 Internal 16-bit MCA slot (ESDI ctrl.)
P6 Speaker/battery/LED connector
P7 Mouse port
P8 Keyboard port
P9 Parallel port
P10 DB25 serial port
P11 34-pin floppy connector
P12 HDD15 video connector
P14 40-pin IBM floppy connector?
P15 Exhaust fan connector
P16 Molex power connector (HDD)
P17 Pads for Molex connector (HDD)
P18 Berg power connector (FDD)
P19 Pads for 2x18-pin connector
P20 Pads for video RAM socket?
SW1 Pads for a switch (reset?)
Y1 32.768 kHz? xtal (RTC)
Y2 10.000 MHz xtal
Y3 16.000 MHz xtal
Z1 PGA-132 socket w/ i80386DX-20
Z2 PGA-68 socket for math co-pro
Z5 G2 GC183 DMA ctrl.
Z9 G2 GC181 CPU/Bus ctrl.
Z35 G2 GC182 Memory ctrl.
Z46 BIOS ROM Even "S/802-06"
Z47 BIOS ROM Odd "S/803-06"
Z56-63 30-pin SIMM sockets
Z75 Motorola MC146818A RTC/CMOS
Z76 D8742 K/B ctrl. "S/804-02"
Z81 G2 GC186-PC PIO ctrl.
Z88 TI TL072C op-amp (PC speaker)
Z96 CXK5864BM-10L 8Kx8 SRAM (NVRAM)
Z122 Paradise PVGA1A (alt)
Z125 3 DIP switches (+pads for 2 more)
Z126-133 KM41464AJ-12 64Kx4 (VGA)
Z136 inmos IMSG171P-35C RAMDAC

P17 The second Molex connector is not populated and the +12 V pad is jumped by a thick bodge wire directly to the PSU edge connector. The original +12 V trace was probably too thin to satisfy the HDD/FDD current draw.

Z2 There's a small PCB under the math co-pro socket. It only contains a resistor network and two discrete resistors. (pullups or termination?)

P5 Internal 16-bit MCA slot. Comes with the WD1007V-MC1 ESDI controller pre-installed.

The rest of the board is covered with 74xx glue, a couple PLDs, and a bunch of passives.


Developed by G-2 Inc., also sold as Headland GCK181.

Headland GCK181 Universal PS/2 Chip Set Datasheet
   GC181 - Bus Controller (page 3 physical)
   GC182 - Memory Controller (page 15 physical)
   GC183 - DMA Controller (page 27 physical)
   GC186 - Peripheral Controller (page 49 physical)

Semiconductor User Information Service Newsletters 1988-1989 (page 144 physical) says:
   "LSI Logic's affiliate, G-2, has entered into an agreement with Groupe Bull of France to manufacture an IBM PS/2 compatible chip set. The chip set includes the GC181 CPU bus controller, the GC182 memory controller, the GC183 DMA controller, the GC184 address-data buffer, and the GC186 peripheral controller. The 20-MHz chip set, which will be sampled in the third quarter of 1988, will be fabricated with a 1.5-micron (1.2-micron effective) CMOS process. (25 Jul 1988)"

System Firmware (POST & BIOS)

Firmware stored in EPROM.

ROM Images

All ROMs are AMD Am27C512-155DC, positions Z46/Z47 (even/odd).

S_802-06 / S_803-06 - BULL SYSTEM BIOS Version B1.1a (rev. 5, 09 Nov 1989)

Exhaust Fan Assembly [P]

The construction of the fan assembly is similar to that of the Model 50. Plastic shroud with a fan and small PCB inside. The fan is held in place with a foam, no clips, no screws...

Fan Model [P]

MODEL 109P0912M4021
DC 12 V 0.1 A

Dimensions: 92mm, 25mm thick

SAN ACE 92mm MINI ACE DC Fan Motors Datasheet

Fan PCB "VENTIL." 729059008-00A [P] [P]

The fan PCB has a provision for two passive components (resistor + thermistor?) but neither was populated on the only sample we have seen (possibly a crude temp control?).

Fan Connector Pinout

6-pin card-edge connector on the planar board.

3+12 V4N/C
5+12 V6N/C

Speaker/Battery/LED Assembly

The assembly consists of the support frame, an interconnect PCB, an LED PCB, a speaker, and a battery.

The frame also doubles as an adapter card support.

Interconnect Board "C. INTERCONNEXION" 7290582008-01C [P] [P]

Edge Connector

12-pin card-edge connector on the planar board.

1N/C2Speaker Data
3N/C4GND (Spkr./Batt.) (?)
5"ST" Jumper (?)6Battery+
7Hard-Drive LED-8Hard-Drive LED+
9Power LED-10Power LED+

P2 "LED" - LED Board Connector

2Hard-Drive LED+
3Hard-Drive LED-
4Power LED+
5Power LED-

P3 "H.P." - Speaker Connector

2Speaker Data

P4 "BAT" - Battery Connector

1Physical Key
3Physical Key

"ST" Jumper

Clear CMOS jumper?

LED Board "CARTE LEDS" 7290589008-00A [P] [P]

Contains the Power ("A/M") and Hard-Drive activity ("DISQUE") LEDs.
Plugs into the Interconnect Board.

Battery Pack [P] [P]

The battery pack consists of two Li-Ion 2.5 V non-rechargeable AA cells wired in series to give approx. 5 V total. The cells are stuffed in a box with a 4-pin header connector attached to it via a twisted pair wire.

The pack is wired to the Interconnect Board.

You probably won't be able to get a replacement battery pack, but you can open the original one and replace the cells. Alternatively, you can replace the entire thing with a battery holder or another battery with equivalent specs.

Warning: Never solder directly to a battery/cell. Either buy cells with contacts already attached, get a mini spot-welder, or use a battery holder. Excessive heat may damage the cell and lead to a fire or an explosion! You are doing this at your own risk.

Original Battery

Made by SAFT
Lithium, 5.2 V, 2.3 Ah
BULL 76957876 002


8 Ω 0.4 W

Plugs into the Interconnect Board.

Power Supply [P]

Similar form factor as the Model 50/70 PSU, but bigger.

ASTEC Model No. BM135-3301

Input: 230 V AC, 1.8 A, 50/60 Hz

Output voltages:

Voltage (DC)Pin #Current / Pin
-12 V1500 mA
+12 V3,5,7,9,11,13667 mA
+5 V15-47 odd # only940 mA
DC Return2-48 even # only1000 mA max.
Power Good50

Maximum continuous output power is 135 W.

The pinout is the same as for the Model 50/70 PSU, except for the "System Status" signal on pin 49 that is missing here (hard-drive activity LED on Models 50/70).

Content created and/or collected by:
Louis F. Ohland, Peter H. Wendt, David L. Beem, William R. Walsh, Tatsuo Sunagawa, Tomáš Slavotínek, Jim Shorney, Tim N. Clarke, Kevin Bowling, and many others.

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