Abecedario Tagalog by Pedro Andres de Castro (1776)

Baybayin enthusiasts should read Baybayin: Ortograpiya at mga Tuntunin sa Pagsulat sa Wikang Tagalog ni Pedro Andres de Castro at Salin ni Elvin R. Ebreo with an open mind and benefit from the meticulous work on the evolution of Filipino orthography. This book also contains a very insightful introduction from Virgilio S. Almario; you'll definitely learn why Baybayin is the true name of the Filipino syllabary.

You can download the pdf book Baybayin: Ortograpiya at mga Tuntunin sa Pagsulat sa Wikang Tagalog here. Just click the link and enjoy the read.