There is only a 1-ch UART port on the original Raspberry Pi, once it is used for terminal debugging, no other serial device is allowed. What a poor situation. Now you have 2-ch extra UART, plus 8 programmable GPIOs, just bring this Serial Expansion HAT.

The SC16IS752 is an I2C-bus/SPI bus interface to a dual-channel high-performance UART. It also provides the application with 8 additional programmable I/O pins. This module uses an I2C interface by default, and its device address is hardware configurable by A0 and A1.

Features:

1. Standard Raspberry Pi 40PIN GPIO extension header, supports Raspberry Pi series boards
2. Onboard SC16IS752, expands 2-ch UART and 8 programmable GPIO through I2C, no extra pin required
3. It is stackable up to 16 this module by setting the address jumper, which means up to 32-ch UART
4. Onboard multi LEDs for indicating the UART working status
5. Reserved I2C control pins, allows working with other control boards
6. Comes with development resources and manual (examples in C and python)