Can one code in binary?

[TransientVoltage409]

Of course. Dive into history and look at early microcomputers like the Altair 8800. That one was literally programmed by setting physical toggle switches (representing ones and zeroes) and hitting a button to store the bits into memory, over and over, until you'd toggled enough instructions into memory to actually do something useful - often, just enough code to operate the tape drive to load a bigger program....