“An Arduino is actually powerful enough to emulate a C64. With only a few external components it outputs PAL or NTSC video and can be connected to any TV or composite input of an analog monitor. This is a further development of the Nano VIC-20 project by Jan Ostmann. The core is an emulator function for the MOS 6502/6510 CPU. This executes the 16 kilobytes of kernal and basic ROM code permanently stored in the Arduino’s flash memory.
Since the Uno/Nano has only 2k RAM, which is almost used up by the video RAM and the system itself, the 1k EEPROM there is also used as RAM. PAL or NTSC composite video is generated by a timer interrupt routine which is called every 64ms (PAL) or every 63.5ms (NTSC). This outputs the sync pulses, the front and rear porch and clocks out the visible pixels using the shift register used for serial communication protocols such as UART, SPI, I2C. These three signals are then mixed together by a few external components.”