This RD-6770 rear derailleur is a 10-speed rear derailleur and as such it isn't really used anymore. All current and previous Di2 generations have moved on to 11-speed and 12-speed.
Its low sprocket max is 28T and the top sprocket min is 11T. The max supported front difference is 16T and its total capacity is 33T.
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Has your RD-6770 broken? You cannot just replace that with an 11-speed model - all installed derailleurs must be the same speed.
Read more on upgrading your bike and compatibility on the pages linked below.
Indexing, trimming, or fine-tuning Di2 rear derailleurs is done through micro-adjustment. Read how to set up your Di2 rear derailleur perfectly and ride without those grinding noises.
Bought a new Di2 rear derailleur and need some help installing it? Read how to install the RD-R8050 / RD-R9150 / RD-6870 / RD-9070 Di2 rear derailleurs.
Does your old 10 speed Di2 bike need an upgrade to 11 speed? Want to add Synchro Shifting? This is the definitive Di2 upgrade guide.
Did you know that you can mix Di2 components from different series and categories? Mixing derailleurs is not recommended, but anything else is fair game!
Shimano front derailleur and rear derailleur specifications... what do they mean, really? This page explains all of them, and why they matter.
