Dmitry Grinberg's $3 Springboard Add-On Gets Handspring Visor Hardware Talking to SD Cards

With just three active components, not counting the SD card itself, this low-cost adapter board hooks straight into the Motorola 68k.

Gareth Halfacree
5 months ago β€’ Retro Tech / HW101

Vintage computing enthusiast Dmitry Grinberg has a treat for anyone who's still rocking a Handspring Visor personal digital assistant (PDA) in the 21st century: an adapter which connects an SD card to the Springboard expansion slot for low-cost high-capacity storage.

"When Handspring released the Visor PDA line, the main distinguishing characteristic of it was the Springboard slot. It was an expansion mechanism via which the device could access wireless internet, make phone calls, play MP3s or radio, capture images, or export the displayed screen image to an external monitor," Grinberg explains. "The Springboard slot was very versatile and many accessories for it were made."

The Handspring Visor launched in 1999, one year after Jeff Hawkins and Donna Dubinsky left Palm β€” the company they had co-founded and which had been acquired by 3Com β€” to build rival device. While primarily a pocket-sized personal digital assistant, the Visor range could be paired with an accessory which provided cellphone services β€” making the Visor line, arguably, one of the first true "smartphones" to hit the market.

With just 2MB of on-board memory β€” 8MB in the Visor Deluxe β€” the Visor line is resource-constrained by modern standards, but that's where Grinberg's work comes in. Taking advantage of the forward-thinking Springboard expansion slot, which provides a direct line to the device's Motorola 68k processor, Grinberg has designed a modern but minimalist expansion board which provides a simple SD card interface.

"Handspring published great many documents on how to make proper a springboard device. These contain all the info one needs to create a proper springboard-compatible accessory. The second required part is the ROM to contain the driver. It is required officially, but not checked for by the device.

"If you are willing to be a bit of a pain for the users, however, you can skip the ROM and tell them to load the driver in another way (infra-red or PC-sync)," Grinberg explains. "This would violate the requirements and your module would not be approved by Handspring. Handspring no longer exists, so we can live with that. Not having the ROM onboard allows for a much simpler board and fewer parts. A win!"

While an initial design failed to work due to other traffic on the 68k bus, Grinberg was able to come up with a solution with the use of just three 74-series SOT-23-packaged logic chips β€” twp D-type flip-flops as latches and an inverter. Using existing patches to PalmOS and a new slot driver for hardware configuration, Grinberg successfully added more storage to the device β€” with boards buildable for just $3.

This is far from Grinberg's first experiment with vintage palmtop devices. His "rePalm" project aims to port the PalmOS personal digital assistant operating system to modern hardware, most recently adding support for the Raspberry Pi Pico and other RP2040-based devices β€” despite having only 264kB of on-chip RAM to play with.

"With my driver, any Handspring device with this $3 board can now read/write SD cards, and so can all PalmOS applications. This same cheap SD-card-interfacing method can be used for any other 68k device," Grinberg says. "The license is simple: free for all non-commercial use."

Links to the hardware designs and software sources and binaries are available on Grinberg's web page.

Gareth Halfacree
Freelance journalist, technical author, hacker, tinkerer, erstwhile sysadmin. For hire: freelance@halfacree.co.uk.
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