Softwareserial RX not working in pins E0 (SWC) and E2 (SWD) ?

[hmeijdam]

For my application it would be nice to use the SWD (E2) pin as a softwareserial pin.

I can use the SWD pin as analog input (A7) and as digital pin (23 or E2), and as Softwareserial TX, but I cannot use it for softwareserial RX.

Is this a known limitation for softwareserial RX?
I saw in the notes in the softwareserial example sketch that e.g. on a Leonardo and Mega not all pins support pinchange interrupt and therefore cannot be used as RX pin.

Hans

[LaZsolt]

I think I found a possibile solution. If the SWD and the SWC is disabled before initializing Software serial, then it may could work.
Disabling SWD and SWC, must write MCUSR twice within 4 clocks:

uint8_t newsr = MCUSR | _BV(SWDD);
MCUSR = newsr;
MCUSR = newsr;

[youxiaojie]

by the way, does this two pin use standard jtag protocol?

[SuperUserNameMan]

Maybe you could help us find the datasheet ?

I tried using Baidu once, but since I don't read/write chinese, I failed.

---

Also, this project ( forked from this project ) contains a software implementation of the protocol.

Maybe it could give you some clues ?

[youxiaojie]

the datasheet is chinese, only one translated:( maybe you have.

[SuperUserNameMan]

the datasheet is chinese, only one translated:( maybe you have.

We can use google-translate. It is ok.

We already have these datasheet :

• LGT8F328p v1.04 and v1.05
• LGT8F328d v1.0.5
• LGT8F88a v1.1.1

But none of them contain information about the SWD protocol ( " SWD双线片上调试/量产接口 " / " Serial Wire on-chip Debug(SWD) " ).

Maybe it is part of an other chinese datasheet ?

[youxiaojie]

but i see there is homemade arduino based isp, how did they achieve this?

[SuperUserNameMan]

the original arduino based ISP seems to come from LGT : https://github.com/LGTMCU/LarduinoISP