This document describes the hardware features of the ST23YT66 smartcard MCU, including the enhanced 8/16-bit ST23 CPU core, 16 Mbytes of linear addressable memory, 210 Kbytes of User ROM, 6.2 Kbytes of User RAM, 2 Kbytes of NESCRYPT RAM, and 66 Kbytes of User EEPROM.