Pin / port choice for usb data

General discussions about V-USB, our firmware-only implementation of a low speed USB device on Atmel's AVR microcontrollers
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Pin / port choice for usb data

Post by shiona » Sun Jan 31, 2016 10:48 pm

I'm creating my first v-usb project.
Attiny24 ended up as my µC of choice.

On the main page I found:
No UART, timer, input capture unit or other special hardware is required (except one edge triggered interrupt).

Also makes no mention of any hardware requirements about pin selection.

Unable to find any realiable source, I looked up multiple schematics of different V-USB projects and it seemed everyone
was using INT0 connected to D+, so I did so too. This is PB2 on the device. PB0-1 are XTAL and PB3 is RESET', which I
would prefer not to disable. That meant D- would have to go to port A. PA0 was the closest pin to trace to, so I went with that.

Now, after designing the board, etching, sourcing the parts and soldering, I came across ... al-part-3/
which cites some code which gives me the impression D+ and D- are required to share the port.
Is this the case?

I do have PA1-2 free, can I use them somehow to save my situation?

After posting I found out that yes, the fear in my original post is true. This information is hidden inside usbdrv.h.
I believe sharing the information about this limitation with potential users would be fair.

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Re: Pin / port choice for usb data

Post by horo » Mon Feb 01, 2016 7:16 pm


Have a look: (Scroll down to "Other interrupts than INT0 for USB")

Ciao, Martin

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