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“There is an odd famine of information about this particular subject available in text form. If you google “usbasp tpi” and things like it, you’ll find posts on the avr forums filled with incorrect information and schematics. This post …
Content for AVR TPI
The Atmel Tiny Programming Interface (TPI) consists of two layers, the access layer and the physical layer. The TPI physical layer supports two modes of operation, transmit and receive. By default, the physical layer is in receiving mode, and waiting for a start bit. The TPI access layer controls the mode of operation.