In 1998 the founders of Palm had a bit of a falling out with the wildly successful PDA company’s new owners. They set up a new company called Handspring, which enabled them to make PDAs again in the way they preferred, This resulted in the Handspring Visor line of PDAs, which featured a big cartridge slot called the Springboard Expansion slot. Much like a Gameboy, you could put in a range of modules, ranging from games to cameras to memory expansion and more. Since these modules connect directly to the internal Motorola 68k-based microprocessor, you could make a module either to comply with this standard or if you’re like [Dmitry], you’d figure out a way to get an SPI device like an SD card to communicate and expand storage.
Editor note: Dmitry’s design isn’t the first SD/MMC interface for the Visor. Portable Innovation Technology’s SD MemPlug Module supported SD/MMC way back in 2002. However – MemPlug was a commercial product, while Dmitry’s work is open source.
Schematic of Dmitri’s SpringSD board for Handspring Visor PDAs.
To make the M68k bus traffic look somewhat SPI-like to an SPI slave, a CS signal had to be generated using a 74LVC1G80GW D-type flipflop, with the same flipflop also used on the address line for MOSI to keep this stable on the side of the SD card. Finally, an inverter (74HCT1G04GW) was added for the clock signal, making for three SOT-23 packages total. All that was required now was a driver to use this custom board. Once the driver was done, [Dmitri] was able to ..
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