Additional information and document update here on my site
https://www.mischianti.org/2019/01/14/esp-01-modules-programming-board/
ESP-01 is low cost esp8266 module, with built-in WIFI.
It was created as Arduino WIFI module, but It's more power than an Arduino, than now if you must do a little module to control a relay or some simple digital datalogger It's the best solution.
Exists some variant of this module, but all have a processor L106 32-bit RISC microprocessor core based on the Tensilica Xtensa Diamond Standard 106Micro running at 80 MHz, when you buy one of It you must pay attention only on Flash, some have 512 KiB Flash, other 1MiB
Pin Definition
This process is tedious, you must connect then remove connection and so on, and to use all pins It's very tedious.
My solution to this problem is to create a programming board (I'm fan of service board).
The functionality is:
I'd like to add the result of my old glorious router (created with an epson scanner and printer), quite rough but ok.
There is also a bug fixed by wire (in the file I give you is no more present).
The usage is quite simple:
First insert esp01 in the board, than connect GND to GND, TX to RX and RX to TX of TTL to USB converter.
Now you are ready to program, I add some usage examples.
Upload a blink file