FIC-486-GAC-2 Cache Module reproduction
Sram is an open-source printed circuit board by raszpl, from the raszpl/FIC-486-GAC-2-Cache-Module repository on GitHub, published under the GPL-3.0 licence. It is a 4-layer board of 90.8 × 33.2 mm with 24 parts on 95 nets, routed with 1,720 tracks and 203 vias.
It is built around the 74F244D and IS61C256AL-12JLI. Its parts include 6 resistors, 2 ICs and 1 connector.
Reverse Engineered non standard 256K L2 Cache Module for use in:
Potentially also:
Incompatible platforms also reusing VLB slot for Cache:
Pictures of the original "DOC: 13630" "ASSY: 008-0078204 A" Cache module:
rev 2 front 
Vogons: FIC 486-GAC-2 proprietary cache module - open source reproduction Completed thread:
majestyk: "FIC sold two different versions with different pinouts (and the same "VLB"-socket). Only the one in the pictures works on a 486-GAC2 and a few other FIC mainboards."
This project was only possible with help provided by majestyk - owner of this very rare Cache module, and RockstarRunner - FIC 486-GAC-2 owner looking for said Cache module. Huge thanks for taking time to capture high resolution pictures and validating progress with measurements.
UMC UM61256A 32K x 8 Static RAM datasheet
VESA VLB slot pinout VESA VLB slot dimensions
100%. Manufactured and tested. Preliminary design took 8 days. Fixes after assembling first prototype 2 days.
4/19/2024: Rev 2.4 assembled by swapping components from Rev 2.2. CACHECHK screenshot.
4/15/2024: Rev 2.4 'Pcbs turned up! We have edge connectors this time 😆'
3/23/2024: Final Rev 2.4. Reworked SRAM footprint for easier hand soldering, slightly optimized capacitor placement.
2/29/2024: Final Rev 2.3. Slightly thicker tracks and silkscreen text, additional clearance work. Shrank from initial prototype, should be almost equal height of original. Height when inserted 26.3mm, height including slot 33.6mm.
2/28/2024: Prototypes assembled after sanding off soldermask from edge slot contacts, didnt work at first try. Turns out I swapped few power/ground pins in the connector resulting in dead short. Great sleuthing by Miisalo uncovered this mishap, after cutting bad connections we have sucessfull boot.
2/27/2024: Prototypes arrived. Who can spot the problem?
Will require some finessing with sandpaper to uncover edge slot pads :)
2/11/2024: 99% done, ERC&DRC 0 errors 0 warnings. Footprints should be correct now. Gerbers sent for manufacturing.
2/8/2024: 95% there, 0 errors, 7 Warnings. 5 connections missing, 11 guesses and assumptions on U1 U2 and some more on common lines.
2/6/2024: 90% there, 0 errors 18 warnings. Just a couple tracks left.
2/5/2024: 80% there, 0 drc errors, 62 violations. Still bad footprints and I havent gotten around to fixing power/ground pins. Whats left is figuring LS244 address buffering mapping, TAG ram address and output pins to edge mapping, WE/CE/OE mapping to edge.
2/4/2024: Very VIP, only about 50% there at the moment.
02/3/2024: Project start. Figuring out how to make edge connector footprint, searching for SOJ-28L footprint.
Interested in having a piece of hardware reverse engineered/cloned? Drop me an email.
| Qty | Value | Footprint | References |
|---|---|---|---|
| 9 | IS61C256AL-12JLI | footprints:SOIC-28 very wide | M1, M2, M3, M4, M5, M6, M7, M8, MD1 |
| 4 | 1uF 16V | Capacitor_SMD:C_0805_2012Metric | CB1, CB2, CB3, CB4 |
| 3 | 0ohm | Resistor_SMD:R_0805_2012Metric | R1, R3, R5 |
| 3 | NC | Resistor_SMD:R_0805_2012Metric | R2, R4, R6 |
| 2 | 47uF 16V | Capacitor_SMD:C_1206_3216Metric_Pad1.33x1.80mm_HandSolder | CT1, CT2 |
| 2 | 74F244 | Package_SO:SOIC-20W_7.5x12.8mm_P1.27mm | U1, U2 |
| 1 | Cache_slot | footprints:Cache slot | J1 |
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It measures 90.8 × 33.2 mm and has 4 copper layers, 1.6 mm thick.
24 parts, built around the 74F244D and IS61C256AL-12JLI. 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.
From the raszpl/FIC-486-GAC-2-Cache-Module repository on GitHub, at the commit this page was made from: the board is sram.kicad_pcb and its schematic sram.kicad_sch. PCBKit opens the board in the browser, with nothing to install.
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).
