Resurrecting Analog: Writing a SCSI Driver for Vintage Film Scanner on Mac SE/30

In an era where obsolescence often condemns hardware to landfills, one developer embarked on a mission to resurrect a 1997 Epson FilmScan 200 scanner for modern use – not through virtualization or adapters, but via a vintage Mac SE/30 running System 7. The scanner's SCSI interface posed the first challenge: its official drivers only supported Mac System 7/8 or Windows 95/98, and modern alternatives like USB-SCSI adapters proved unreliable.

The FilmScan 200 scanner alongside the Mac SE/30 used for development.

Decoding the Hardware

Armed with a service manual, the developer uncovered critical specifications:

Spec	Value
SCSI device type	“Processor” (0x03)
Protocol	ESC/I commands via SCSI SEND/RECEIVE
Max resolution	1200 DPI
Frame size	1120x1680 pixels

The scanner’s designation as a "Processor" was unusual—unlike standard scanners, it used generic SCSI commands (SEND 0x0A, RECEIVE 0x08) to shuttle ESC/I protocol data. Excerpt from the scanner's service manual.

Building the Driver

Using THINK C 5.0 on the SE/30, development began with the SCSI Manager API—a complex sequence requiring precise error handling:

SCSIGet(); 
SCSISelect(); 
SCSICmd(); 
SCSIRead(); 
SCSIComplete();

The initial breakthrough came with a monochrome scan sequence:

1. Initialize scanner (ESC @)
2. Set mono mode (ESC C 0x00)
3. Configure resolution (ESC R)
4. Define scan area (ESC A)
5. Start scan (ESC G)

First successful monochrome scan saved as PGM file.

The Frame Selection Puzzle

Attempts to scan frames beyond #1 failed despite disassembling Epson’s 68K driver. The breakthrough came from an obscure SANE driver patch discovered on a decades-old website:

// SANE driver revelation:
simplecommand(SET_BAY, s, s->val[OPT_BAY]+1, s->val[OPT_BAY]+1);

The solution? Send the frame number twice in the command (e.g., [2,2] for frame 2), bypassing the original driver’s undocumented validation handle.

Cracking Color Scanning

Color mode (ESC C 0x02) revealed another layer: data arrived in non-interleaved GRB order across three separate blocks per line:

for (i = 0; i < width; i++) {
    output[i*3]   = rBuf[i]; // Red
    output[i*3+1] = gBuf[i]; // Green
    output[i*3+2] = bBuf[i]; // Blue
}

Mixing up the channel order initially produced surreal green-tinted results before correction.

The Workflow

The film carrier holds six frames. The final driver:

• Scans batches of 1-6 frames
• Saves as PPM/PGM files
• Transfers via FTP to modern systems A 6-frame color scan takes ~10 minutes—a testament to the SE/30’s enduring capability.

Why This Matters

Beyond nostalgia, this project underscores critical lessons for modern developers:

1. Documentation longevity: Service manuals enabled reverse-engineering that binary disassembly alone couldn’t solve.
2. Protocol assumptions: 0 vs. 1-indexing and parameter formats remain subtle failure points.
3. Sustainable tech: Legacy systems retain utility in specialized workflows when given purpose-built software.

The driver (available on GitHub) transforms obsolete gear into a functional digitization pipeline—proving that with curiosity and C, even analog film can find a path through 30-year-old silicon.