Updated USBspi bridge adapter

USBspi is a general purpose SPI bridge for USB designed by ChaN. Adapted have been updated from older one by replacing older MCU to Attiny2313 and instead COM port there is USB adapter attached which works through FT232RQ USB to RS232 bridge. So writing time is faster now.


Also adapter board is placed in small box because of Attiny2313 MLF package is used. Earlier version looks like this.

Circuit diagram

In this version the power supply can be selected “From target” or “To the target” from USB port.



The serial to SPI bridge has two different operating modes, Cooked Mode and Through Mode. The operation mode can be changed by ER (DTR) signal at any time.

  • In Through Mode (ER on) – When ER goes on, serial to SPI bridge enters the Through Mode. In this mode, the data signals are passed through the bridge. This enables to communicate between PC and target with any generic terminal program in software implemented UART. It will be useful for debugging and maintenance work. The output drivers on the SPI signals, RESET, SCK and MOSI, can be switched by a disconnect switch.

  • In Cooked Mode (ER off) – When ER goes off, the serial to SPI bridge enters the Cooked Mode. In this mode, the bridge is controlled by PC in a defined protocol. The protocol is determined on future compatibility and minimum changes to existing programming tools for avrspi adapter; as a result, it does not have any block operation, most commands correspond to single SPI transaction and it can also do pipelined operation.

Download newest version of documentation here: SPI bridge Rev.2 document

Source: https://elm-chan.org/works/avrx/report_e.html



  1. Pingback: Electronics-Lab.com Blog » Blog Archive » Updated USBspi bridge adapter

  2. Thanks beautiful share

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