TriGem · SX386
TriGem SX386M
TriGem OEM motherboard with a 16 MHz 80386SX, Headland chipset, IDE and six ISA slots.
EXPERIMENTAL: POST with 4 MB, CMOS configuration and MS-DOS 6.22 boot are validated. The 8 MHz low-speed mode is implemented as an approximation and untested. All RAM populations, shadow, EMS and parity/NMI still need validation; the exact peripheral chips and the keyboard-controller ROM are unknown.
History
TriGem built this SX386M board, revision KS-II, for other companies' computers, such as the Emerson Elite SX386/16 and the CMS Enhancements ESP SX386M. It is not an Olivetti model or a rebadged Olivetti. Epson's guide to the 20 MHz version describes another TriGem revision.
Hardware
- Processor
- Intel 80386SX 16 MHz; 8 MHz low-speed mode
- Memory
- 512 KB to 8 MB parity DRAM, documented 30-pin SIMM populations
- Video
- External ISA display adapter
- Floppy drive
- Integrated AT-compatible floppy interface
- Clock and CMOS
- 128-byte AT-compatible CMOS RTC; exact component unconfirmed
- Math coprocessor
- Intel 80387SX optional; J2 enables/disables it
- Expansion slots
- 4 × 16-bit ISA + 2 × 8-bit ISA
- Interfaces
- IDE, floppy, two serial, parallel and AT keyboard
- Dimensions and weight
- 254 × 218 mm OEM motherboard
Catalogue classification
- Form factor
- Desktop
- Mobility
- Stationary
- Processor generation
- 80386SX class
- Storage interface
- Floppy drive, IDE
Research
This page separates documented hardware facts, behavior observed in original firmware, and the current fidelity of BluMach emulation.
Architecture and memory
Evidence: documented or confirmed hardware
- CPU and bus
Intel 80386SX at 16 MHz with documented 8 MHz low-speed mode; optional 80387SX.
- Memory
Parity DRAM: documented populations of 512/640 KB and 1/1.5/2/3/4/4.5/5/6/8 MB. The BIOS encodes the bank configuration in the HT113 and BluMach uses the same encoding for all of them. Without shadow, the 384 KB of the hole becomes extended memory; Setup subtracts it when shadow is enabled.
- Main circuits
Photographs identify the Headland HT101SX, HT113 and GC102-PC. BluMach using the same chipset model as for the Olivetti PCS 386SX does not link this board to Olivetti.
- Expansion slots
Four 16-bit and two 8-bit ISA slots; external video adapter.
BIOS and firmware
Evidence: behavior recovered from BIOS code and testing
- Known revisions
AMI DG2X-6080-020491-KB, dated 4 February 1991.
- ROM organization
One 64 KB linear image at F0000h, expected as EESX386.BIN; metadata only, not redistributed.
- Modeled interface
The BIOS probes the HT113 at 1ECh–1EFh, clears 64 registers and programs CR0–CR4, including CR2=DAh; it does not use 92h. BIOS shadow is CR0 bit 4. Video shadow copies C0000h-C7FFFh to RAM and keeps it mapped through EMS page registers 24 and 25, write-protected.
Jumpers and physical configuration
Evidence: documented or confirmed hardware
- Jumper bank
J2 enables 80387SX; JP4 selects LPT1/LPT2; JP6 selects mono/color; RAM follows documented SIMM populations.
- Serial and parallel
Integrated IDE, floppy, two serial ports, parallel port and AT keyboard. The 3F3h latch used by the BIOS delays COM and LPT activation; the exact controller ICs are still being researched.
- Video
Video is provided by an external ISA adapter; the motherboard has no integrated VGA or video firmware.
Emulation status
Evidence: current BluMach status; not necessarily a description of the original circuit
- Verified
Authentic AMI firmware identifies Emerson, completes 4096 KB POST, detects COM1/COM2/LPT without false conflicts, and installs then boots MS-DOS 6.22 from a 40 MB type 17 IDE disk.
- Pending or approximate
Experimental. All RAM populations, System+Video shadow, parity/NMI, low-speed mode and EMS still need validation. Low-speed mode follows bits 2-3 of the keyboard-controller output port (Ctrl+Alt+grey − and grey +, and Start-up Speed in Setup), but is approximated with memory wait states without changing the CPU clock. Exact peripheral ICs are unidentified, so AT-compatible approximations are used. The memory selector still allows undocumented 128 KB intermediate values.
Sources
Sources and traceability
Evidence: primary sources and research notes