This manual deals with the description of the instruction set and addressing modes of ST62,63 microcontroller series. The manual is divided in two main sections. The first one includes, after a general family description, the addressing modes description. The second section includes the detailed description of ST62,63 instruction set. Each instruction is described in detail with the differences between each ST6 series. ST6 software has been designed to fully use the hardware in the most efficient way possible while keeping byte usage to a minimum; in short to provide byte efficient programming capability.