First post, by Paul_V
- Rank
- Newbie
Hi, everyone.
Just got my hands on one this motherboard from aliexpress. It is labeled simply "ISA855" and I managed to find a manual for it.
It is marketed as an industrial motherboard mATX and it's specs vary from one production batch to another.
UPD: revised the first page to be as brief, yet informative, as possible.
Brief Specs
This board may have either s479 socket accepting Celeron-M or Penrium-M, or come pre-soldered BGA.
Seems both 400mhz and 533mhz bus CPUs are supported.
The Pentium-M variant is of the most interest, because it's able to downclock through SpeedStep.
There is a jumper on the motherboard named JP_FSB
Setting that jumper switches FSB clock from 400Mhz to 533Mhz
It can be used as an overclocking or downclocking option for Banias\Dothan CPUs
256MB or 512MB DDR1 RAM (Soldered, no slots, no upgarade possible)
I have not yet seen any boards with 256MB
The RAM itself is soldered (with no SPD chip present either).
This means BIOS is either has some SPD data hardcoded, SPD is hw-strapped, or it just skips the checks altogether.
Absebce of an SPD chip makes it harder to find a compatible BIOS from another motherboard with simialr chipset.
But the motherboard itself has an unpopulated footprint for an SPD chip. It's located to the right of the top pci slot.
Dumping a ROM from Samsung 512MB DDR1 SO-DIMM and transfering it to a spare 24C02 eeprom proved working. I could successfully read the data from OS.
Upgrading memory to 1GB would probably require soldering 8 new ram IC's and\or new SPD data.
But personally, I do not need that much RAM. And testing this would require a donor board anyway.
Northbridge:
852\855GM (I believe the main northbridge difference is the GPU supported clock\bus speeds)
MoBo defaults to same BIOS / CMOS settings, but actual components on them differ from batch to batch.
This is also valid for GMCH. It can be 852GM, 855GM,855GME or 852GME.
Only the latter supports full bus speeds this motherboard can provide.
For others default BIOS settings and 533mhz bus mean overclocking beyond stable operation and often causes aftifacts and issues.
All 85* series have integrated Extreme Graphics 2 GPU, which supports DirectX7.0 and OpenGL1.3
Memory is shared with onboard RAM
VBIOS is integrated into main BIOS.
SouthBridge:
ICH4M
PCI-to-ISA Bridge:
IT8888, provides two ISA slots with DMA support
The main BIOS is Award BIOS 6.00PG
Firmware slightly differs from batch to batch, mainly concerning option ROMs and CPU microcodes.
Some are missing both LAN option ROMs and microcodes.
VBIOS ROM is programmed to hold mostly widescreen panel resolutions.
LVDS 18bit 1ch:
640x480
800x480
800x600
1024x600
1024x768
1280x800
1366x768
LVDS 18bit 2ch:
1600x900
LVDS 24bit 1ch:
1024x768
1280x800
1366x768
LVDS 24bit 2ch:
1440x900
1600x900
1680x1050
1920x1080
2048x1536 (hidden in BIOS and probably not supported by hardware)
Using CRT+LVDS option and a panel resolution in BIOS forces the chosen resolution to persist in DOS mode.
VBIOS can hold 16 panel timings which can be edited through Intel BMP tool to add custom timings\resolutions.
VBIOS ROM itself can be exported and swapped from another 855GM board through Award CBROM tool.
This way I've been able to add 1600x1200 and 1900x1200 to achieve good scaling in native DOS.
ALC655 AC'97 Codec
Compatible with SBEMU
This motherboard has an AC'97 standard compatible internal 8pin connector.
By default, there are two jumpers, which basically connect ALC655 R\L output to rear panel audio jack.
This provides a solution to connect a custom or any other ISA soundcard output to these pins though a switch, toggling rear panel output between ALC655 and ISA soundcard.
I'm planning to implement this on my build with a custom made internal soundcard, making possible to switch between soundcards.
RTL8100C LAN IC. as I'm aware, is compatible with DOS.
Some BIOSes are missing an option ROM for it, making PXE boot unavailable.
You can add your own option rom through CBROM
Proprietary 12V power input - 3.96mm 2-pin JST or 4-pin 12v ATX molex
4-pin MOLEX connector at the bottom of the motherboard is power output for HDD, not input.
5v and 3.3v are generated by the motherboard and thus have more strict power draw limits.
There is a jumper to switch between AT \ ATX power button behaviour.
Basically, any decent 65w or higher 12v laptop power brick could be converted to power this board.
I would stay away from cheap ones or LED stripe PSUs.
Motherboard revision v1.1 has through-hole toroidal inductor coils, which emit audible high pitch noise.
They are replacend by epoxy filled SMD ones in v1.3, reducing overall noise
1) JP_FSB jumper to switch FSB between 100Mhz(400) and 133Mhz(533).
2) "MGMT Core Frequency" in BIOS (FSB/MEM/GFX LOW/GFX HIGH core freq)
3) Pentium-M SpeedStep (setting multiplier from x6 to a max supported by CPU (e.g. x16 for 1.6 GHz Banias Pentium-M at 100Mhz(400) bus)
4) On Demand Clock Modulation - 1/8 to 8/8
5) ICH4 chipset throttling - 1/8 to 8/8
6) L1 Cache on\off
The last four from the item list can be toggled on-the-fly though an awesome CPUspd utility.
1) USB support in DOS is wonky, so PS/2 is a way to go. Moreover, CPU or chipset throttling often makes USB inoperable.
2) CF card slot pin quality is poor. Pins tend to bend and pop out from another side of the slot while inserting the card.
3) Stock CPU fan is quite loud and the motherboard has no PWM, needs replacement.
4) Proprietary 12V power input - 3.96mm 2-pin JST or 4-pin 12v ATX molex. Which means other voltages like 5v and 3.3v are generated by the motherboard and have more strict power draw limits.
5) Issues booting from USB stick. The screen freezes on "Verifying DMI Pool Data".
Currently, no universal solution. The root problem seems to be the BIOS. You could try following:
- Use another software to create bootable usb
- Choose another usb flash, preferrably 2.0
- Use a USB to CF adapter as a USB stick for Rufus (mostly worked for me)
- Use plop boot manager and set it to ignore first usb device in the list and manually boot the second
AMIBIOS8 generally has better USB boot compatibility than AWARD, but I could not port AMIBIOS8 to this board as of yet.
6) 44-pin IDE DOM should have pins to select MASTER\SLAVE device. Otherwise it may freeze the system on boot.
7) If you are experiencing stability issues or having artifacts, it may be due to wrong HW straps or BIOS settings.
Removing JP_FSR jumper will set the FSB from 133 to 100Mhz.
8) As reported, FX5500 GPU is not compatible with this motherboard.
So, here it is. A lovely piece of a versatile retro hardware in a small (so-to-speak) package. It has all the advantages of a laptop Pentium-M CPU\Chipset and throttling speed is fluid.
But getting the one with the specs you want is a gamble.