> 4-bit wide bus that real controllers can use
>=20
> Is it easy to bit-bang this on PICs/dsPICs/PIC32s?

Assuming that have the resources to process 4-bit parallel data, you
should be able to improve on serial SPI speed

https://www.sdcard.org/developers/tech/pls/

Click 'I Accept' to get to

https://www.sdcard.org/developers/tech/sdcard/pls/simplified_specs/

Part 1, Physical Layer Simplified Specification Version 3.01 describes
the Bus Protocols in Section 3.6

Joe


--=20
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