You can’t make use of all of these at once, but with up to four different connections wired to a single pin you can ... As for UARTs, the Raspberry Pi’s one-and-a-half UART interface has ...

we have built a board which simply connects through the Pins on the Raspberry Pi as usual, but include access to extra UART’s without limiting the Pi any further or without a special image.

or 2 stop bits as well as offering support for all Raspberry Pi Model B and A system using a 26 Pin ribbon cable. Salicon Technologies explains : “UART HAT is Add-on board for Raspberry Pi ...