That’s because its internally hooked up to the ESP8266’s SPI flash chip, ... In Circuit Programming is still my favorite, and you only need 4 pins (3.3V, TX, RX and GND), ...

The MS-DOS 3.3 bootdisk image is stored in flash and is accessed ... 80×25 characters on a 3.5″ TFT display with the help of a low pass filter circuit. ... PC-XT Emulator On ESP8266 ” ...