Is it possible to emulate a usb serial on nrf51x22 ?

[Jie]

Hi.

nrf51x22 has 32 IOs. can we assign 2 pin to usb d+, d-, and listen interrupt.

yes, nrf51x22 has uart support, but many host device only have usb port. serial port has miss a long time.

USB have power supply, and could communication with host device. it is very important.

there have any idea to implement USB in nrf51x22?

[RK]

I wouldn't bother trying to bitbang USB. The protocol is sufficiently complex it's hard to get right. There's probably libraries you can find which you could use, but the timing requirements are such it wouldn't likely work with the softdevice running anyway.

Buy a chip which does USB, like an FTDI, and hook it up over I2C or SPI or whatever you like to the nrf51x22.

[Wojtek]

You can find some clues here, but I'd also don't recommend bitbanging as You still need some physical elements to meet electrical requirements. Using FTDI-like chips is just much simplier.

[RK]

That link brings up another point I forgot to mention. USB 1.1 speed is 1.5Mb/s, that's the old old USB. At that speed on the nrf51 series you have 10 machine instructions per transmitted bit. That's really not very much, it's possibly not even enough.

That reminds me again what a great job the integrated USB chips do.