INTRODUCTION
The ST72T121 HCMOS Microcontroller Unit (MCU) is a member of the ST7 family. The device is based on an industry-standard 8-bit core and features an enhanced instruction set. The device is normally operated at a 16 MHz oscillator frequency. Under software control, the ST72T121 may be placed in either Wait, Slow or Halt modes, thus reducing power consumption. The enhanced instruction set and addressing modes afford real programming potential. In addition to standard 8-bit data management, the ST72T121 features true bit manipulation, 8x8 unsigned multiplication and indirect addressing modes on the whole memory. The device includes a low consumption and fast start on-chip oscillator, CPU, program memory (OTP/EPROM versions), RAM, 32 I/O lines, a Low Voltage Detector (LVD) and the following on-chip peripherals: industry standard synchronous SPI and asynchronous SCI serial interfaces, digital Watchdog, two independent 16-bit Timers, one featuring an External Clock Input, and both featuring Pulse Generator capabilities, 2 Input Captures and 2 Output Compares (only 1 Input Capture and 1 Output Compare on Timer A).

■ User Program Memory (OTP/EPROM): 8 to 16K bytes
■ Data RAM: 384 to 512 bytes including 256 bytes of stack
■ Master Reset and Power-On Reset
■ Low Voltage Detector (LVD) Reset option
■ Run and Power Saving modes
■ 32 multifunctional bidirectional I/O lines:
   – 9 programmable interrupt inputs
   – 4 high sink outputs
   – 13 alternate functions
   – EMI filtering
■ Software or Hardware Watchdog (WDG)
■ Two 16-bit Timers, each featuring:
   – 2 Input Captures and 2 Output Compares 1)
   – External Clock input (on Timer A)
   – PWM and Pulse Generator modes
■ Synchronous Serial Peripheral Interface (SPI)
■ Asynchronous Serial Communications Interface (SCI)
■ 8-bit Data Manipulation
■ 63 basic Instructions and 17 main Addressing Modes
■ 8 x 8 Unsigned Multiply Instruction
■ True Bit Manipulation
■ Complete Development Support on DOS/WINDOWSTM Real-Time Emulator
■ Full Software Package on DOS/WINDOWSTM (C-Compiler, Cross-Assembler, Debugger)