INTRODUCTION
The W541E261 and W541C261 are high-performance 4-bit microcontroller (μC) with an LCD driver and the flash EEPROM and mask ROM for the program memory. The device contains a 4-bit ALU, two 8-bit timers, two dividers, a 32 × 4 LCD driver, and five 4-bit I/O ports (including 1 output port to drive the LEDs). There are also five interrupt sources and 8-level subroutine nesting for interrupt applications. The W541E261 and W541C261 have two power reduction modes, hold mode and stop mode, which help to minimize power dissipation.

FEATURES
• Operating voltage: 2.4V to 5.5V (LCD drive voltage: 3.0V, or 4.5V)
• Operating frequency up to 4 MHz
• Crystal/RC oscillation circuit selectable by code option for system clock
• Memory
    − 2048 × 16 bit program ROM (including 2K × 4 bit look-up table)
    − 128 × 4 bit data RAM (including 16 working registers)
    − 32 × 4 LCD data RAM
• Single or Dual Clock Mode
    − Single (main oscillator only) or dual clock (both main and sub-oscilator) by mask option .
    − Dual-clock slow operation mode: system is operated by the sub-oscillator (FOSC = Fs and Fm is stopped)
    − Sub-oscillator is only 32.768 KHz crystal for dual clock mode.
    − Main oscillator is crystal or RC oscillation by mask code option .
    − Main clock : High-frequency clock (400 KHz to 4 MHz) or low-frequency clock (32.768 KHz) is selected by mask code option.
• 21 input/output pins
    − Ports for input only: 2 ports/8 pins
    − Input/output ports: 2 ports/8 pins
    − Port for output only: 1 port /4 pins (high sink current to drive LEDs)
    − MFP output pin: 1 pin (MFP)
• Power-down mode
    − Hold function: no operation (except for oscillator)
    − Stop function: no operation
• Five types of interrupts
    − Four internal interrupts (Divider 0, Divider 1, Timer 0, Timer 1)
    − One external interrupt (Port RC)
• LCD driver output
    − 32 segment × 4 common
    − Static, 1/2 duty (1/2 bias), 1/3 duty (1/2 or 1/3 bias), 1/4 duty (1/3 bias) driving mode can be selected
    − LCD driver output pins can be used as DC output ports; selectable by code option
• MFP output pin
    − Output is software selectable as modulating or nonmodulating frequency
    − Works as frequency output specified by Timer 1
• Two built-in 14-bit clock frequency divider circuit (divider 0 and divider 1)
• Two built-in 8-bit programmable countdown timers
    − Timer 0: one of two internal clock frequencies (FOSC/4 or FOSC/1024) can be selected
    − Timer 1: includes an auto-reload function; and one of three internal clock frequencies (FOSC or FOSC/64,Fs) can be selected or falling edge of pin RC.0 can be selected (output through MFP pin)
• Built-in 18/14-bit watchdog timer selectable for system reset
• Powerful instruction set: 120 instructions
• 8-level subroutine (include interrupt) nesting
• Up to 1 μS instruction cycle (with 4 MHz operating frequency)
• Packaged in 80-pin QFP