2 layers232.8 × 204.2 mm
4 layers222.3 × 85.7 mm
386 memory board simm
ronnyroy111/386-memory-board1recreated memory expansion board for the Intel 301 386 mainboard
- Size
- 222.3 × 85.7 mm
- Copper layers
- 4
- Thickness
- 1.6 mm
- Parts
- 78
- Nets
- 373
- Pads
- 926
- Tracks, vias
- 1,894, 360
- Pours
- 5
- Routed
- Yes
- KiCad
- KiCad 9.0 (file 20241229)
- Created
- 3 Nov 2024
- Updated
- 1 Jun 2025
Overview
386 memory board simm is an open-source printed circuit board by ronnyroy111, from the ronnyroy111/386-memory-board repository on GitHub, published under the GPL-3.0 licence. It is a 4-layer board of 222.3 × 85.7 mm with 78 parts on 373 nets, routed with 1,894 tracks and 360 vias.
It is built around the 74LS158DC, 74LS174DC and 74LS04PC. Its parts include 34 capacitors, 28 ICs and 3 connectors. It belongs with the computers and single-board computers boards of this library.
Main components
374LS158DC
CDIP-160℃~+70℃ 4.75V~5.25V 400uA 74LS 7ns 8mA Reverse function Single Supply CDIP-16 Signal Switches, Multiplexers, DecodersTexas InstrumentsSignal Switches, Multiplexers, Decoders
74LS174DC
-0ns 0℃~+70℃ 1 16mA 20ns 30MHz 30ns@5V,15pF 4.75V~5.25V 400uA 6 74LS Series 8mA Asynchronous Push-Pull Reset Rising Edge - Flip Flops ROHSonsemiFlip Flops
74LS04PC
PDIP-140℃~+70℃ 4.75V~5.25V 6 6.6mA 74LS PDIP-14 InvertersonsemiInverters
README
README.md386 memory board by ronnyroy
This is an attempt to reproduce and improve the 32 bit memory expansion cards of the Intel 301 386 mainboard https://theretroweb.com/motherboards/s/intel-301-system-board-pba-451213-xxx based off my original 2MB card.
Instead of 41256 DIP DRAM chips it uses 30pin SIMM modules, all SMD parts and can also be adapted to 8MB.
Big thanks to i440bx who was working on reverse engineering his own card independently and helped greatly by finding the user manual for the board and an image of the 8MB card on https://www.vaxbarn.com/index.php?option=com_content&view=article&id=749.
Initial Revision
The initial PCB revision has been tested and confirmed working.
It was designed to test my clone of the 2MB card and for modding it to 8MB.
Modding to 8MB
- CPUA21(pin85) on the slot to pin 5 of U9 and U16.
- CPUA22(pin95) on the slot to pin 4 of U10 and U13.
Second Revision
This adds the missing traces and jumpers required for 2/8MB operation and the slot cutout i excluded from rev.1.
Important!
An 8MB card configured to 2MB on the mainboard will start up fine and even pass an extended CheckIt memory test but running programs that use the memory of the card crash.
So the card needs to be configured matching to the mainboard.
Parts
78| Qty | Value | Footprint | References |
|---|---|---|---|
| 24 | 100nF | Capacitor_SMD:C_0805_2012Metric_Pad1.18x1.45mm_HandSolder | C1, C2, C3, C10, C11, C12, C13, C14, C15, C16, C17, C18, C19, C20, C21, C32 +8 |
| 10 | 10µF | Capacitor_SMD:C_1206_3216Metric_Pad1.33x1.80mm_HandSolder | C22, C23, C24, C25, C26, C27, C28, C29, C30, C31 |
| 10 | 33Ω | Resistor_SMD:R_Array_Concave_4x0603 | RN1, RN2, RN4, RN7, RN8, RN9, RN10, RN11, RN12, RN13 |
| 6 | 74LS158 | Package_SO:SO-16_5.3x10.2mm_P1.27mm | U7, U8, U9, U14, U15, U16 |
| 6 | 74LS174 | Package_SO:SO-16_5.3x10.2mm_P1.27mm | U5, U6, U10, U11, U12, U13 |
| 4 | 74F10 | Package_SO:SO-14_5.3x10.2mm_P1.27mm | U17, U37, U40, U44 |
| 4 | ~ | 386_memory_board:DOUBLE-SIMM-30 | U1, U2, U3, U4 |
| 2 | 74F00 | Package_SO:SO-14_5.3x10.2mm_P1.27mm | U38, U39 |
| 2 | Conn_01x02_Pin | Connector_PinHeader_2.54mm:PinHeader_1x02_P2.54mm_Vertical | J2, J3 |
| 2 | MountingHole | MountingHole:MountingHole_3.2mm_M3_DIN965_Pad | H1, H2 |
| 2 | SPARE | Package_SO:SO-16_5.3x10.2mm_P1.27mm | U18, U19 |
| 2 | ~ | Package_SO:SOIC-16W_7.5x12.8mm_P1.27mm | U20, U22 |
| 1 | 74F02 | Package_SO:SO-14_5.3x10.2mm_P1.27mm | U43 |
| 1 | 74LS04 | Package_SO:SO-14_5.3x10.2mm_P1.27mm | U45 |
| 1 | Bus_386_Memory | 386_memory_board:BUS_386_MEMORY | J1 |
| 1 | LOGO | 386_memory_board:i386_compatible_30mm | G*** |
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Questions
How big is the 386 memory board simm PCB?
It measures 222.3 × 85.7 mm and has 4 copper layers, 1.6 mm thick.
What parts does the 386 memory board simm use?
78 parts, built around the 74LS158DC, 74LS174DC and 74LS04PC. The full list of its parts is on this page, with links to each part's symbol and footprint where PCBKit's library has them.
Where can I download the 386 memory board simm KiCad files?
From the ronnyroy111/386-memory-board repository on GitHub, at the commit this page was made from: the board is 386_memory_board_simm.kicad_pcb and its schematic 386_memory_board_simm.kicad_sch. PCBKit opens the board in the browser, with nothing to install.
Can I use the 386 memory board simm design in my own project?
Its repository publishes it under the GPL-3.0 licence: you may reuse it on that licence's terms (keep the author's notice, and for a copyleft licence share your changes alike).