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Tutorial on UART Serial Communication / LPC21xx
Reference : Document UM10139 Chapter 9
UART0/1 Serial Communication Program
Unlike SPI, UART is asynchronous communication protocol. This protocol pulse out data in form of data bauds, each baud consist of some fixed number of bits. As system programmer we can modify the baud rate (bauds per second) following a defined procedure. Most of the registers controlling the UART block are 8 bits wide. Below is a list of registers associated with UART0 .
Details of all above registers can be found in the User Manual UM10139. Most important thing to remember is about Divisor Latch Access Bit. While configuring U0DLL and U0DLM, DLAB bit in U0LCR (Line control register) should be 1. One should clear DLAB bit immediately after configuring Baud rate using divisor Latch registers, as in order to access U0RBR & U0THR, DLAB bit must be 0.