As a developer, it's always been really easy to know what my responsibilities are (and what they aren't). I do tech-related stuff, answer tech related questions, and try to be as articulate as possible at the intersection of the technical stuff and the wider business processes.
With moving into the scrum master role, this has shifted. I'm still developing, but developing nowhere near as much as before. Rather, my standard tool has switched from RAD to JIRA. I'm even finding that RAD remains unopened until time during the day.
I also find myself doing a lot of coordination tasks. The documentation about scrum masters repeatedly use the word 'facilitator', but it seems like coordinator is more appropriate. Perhaps that's indicative of less-than-complete buy in among the team, or simply the teething issues that come with trying to start from scratch. Either way, a lot of time is trying to get the right information from the right people.
The final big thing for me is the sense of responsibility. On the last project where I was purely in a development role, I had the collective commitment attitude, but I knew a lot of what was being done by my Scrum Master was obscured from me. It's a big step up - I have to be the one to make all the things happen that I took for granted when my focus was purely development.