I wrote an application based on a DigiSpark Pro (ATtiny167). My problem is it works on my newer systems and not on the older core 2 Duo based ones. In an effort to gain understanding I loaded the DigiSpark HID keyboard example. It just prints “Hello DigiSpark” in a loop. Like my application, it works on the new and fails on the old. So I loaded it on DigiSpark (ATtiny85) and found it worked on all systems. Obviously there are a few configuration differences in usbconfig.h Other then that all the software, including V USB version, is the same. I have observed that the idle state on the ATtiny85 has D- HIGH and D+ LOW while it is the other way round on the ATtiny167. I don’t know about on the wires but just on the board pins so this could be a red hearing. Anyway, as I understand it this idle state indicates bus speed so I thought it could be related. Any suggestions or insights? Thanks.