What chip provides parallel data to UART circuit?

[m4rtin]

As I understand, UART is an integrated circuit which translated data between parallel and serial forms. While serial data is transmitted to wire(or air in case of BT or IrDA), then what provides parallel data to UART circuit? And in the other end, the serial data is translated back to parallel. What requires this parallel data?

[c4757p]

Microprocessors....

[ejeffrey]

Yes, microprocessors.  Even if the UART is built in, the microprocessor internally has parallel data structures, and the UART serializes them.

That isn't all that UARTs do.  They also have the reclocking logic necessary to handle the asynchronous part of UART, and they have a FIFO to handle the speed rate differential between the MCU and the serial connection.

[ignator]

In my past, PLD or FPGA unloaded the UART, and most recent, the UART digital hardware was sucked into the PLD/FPGA. The processor would dump data into a FIFO RAM, and modify pointers, that the unloader hardware would autonomously pump out and in from the external serial stream. But in the old days it was all microprocessor with interrupt timer that was a function of the UART buffer size, so if it could keep the last two received words, the timer was set to interrupt at 2x the word time period.
Hate to say it but it was the software weenies that wanted to not have to service UART interrupts.

[free_electron]

8251 16550 16450 are a few usarts. ay3-15xx also.