# Physical debug interface - two wire?

**URL:** <https://forums.sifive.com/t/physical-debug-interface-two-wire/1061>\
**Category:** RISC-V\
**Created:** [March 1, 2018, 9:24am UTC](https://forums.sifive.com/t/physical-debug-interface-two-wire/1061 "2018-03-01T09:24:50Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![MikeRJ](https://avatars.discourse-cdn.com/v4/letter/m/46a35a/32.png) [@MikeRJ](https://forums.sifive.com/u/MikeRJ)\
**Post date:** [March 1, 2018, 9:24am UTC](https://forums.sifive.com/t/physical-debug-interface-two-wire/1061/1 "2018-03-01T09:24:50Z")

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Does SiFive have a two wire debug interface (e.g. like SWD on ARM) for the RISC-V, rather than the full JTAG? I am working on an application that is very I/O constrained.

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**Author:** ![joryhuang](https://avatars.discourse-cdn.com/v4/letter/j/b9bd4f/32.png) [@joryhuang](https://forums.sifive.com/u/joryhuang)\
**Post date:** [October 25, 2018, 1:57am UTC](https://forums.sifive.com/t/physical-debug-interface-two-wire/1061/2 "2018-10-25T01:57:47Z")

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I also find this JTAG connection, from their debug spc I find:  
**DTMs are specified for protocols like USB, I2C, SPI, and SWD.**  
but indeed i donot find any description from their E3/5 series SPC