Mixtec writing originated as a logographic writing system during the Post-Classic period in Mesoamerican history. Records of genealogy, historic events, and myths are found in the pre-Columbian Mixtec codices. The arrival of Europeans in 1520 AD caused changes in form, style, and the function of the Mixtec writings. Today these codices and other Mixtec writings are used as a source of ethnographic, linguistic, and historical information for scholars, and help to preserve the identity of the Mixtec people as migration and globalization introduce new cultural influences.
More information on the Wikipedia page  which has links to articles on various codices.