Universal Asynchronous Receiver Transmitter UARTittc.ku.edu/~gminden/Embedded_Systems/Lectures/EECS_388_UART_B40211.pdf• Focus on Universal Asynchronous Receiver Transmitter (UART)

© G. J. Minden 2013

Universal Asynchronous Receiver Transmitter

UART

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Gary J. MindenFebruary 11, 2014


Serial Communications• A few example protocols

• A few example principles

• Focus on Universal Asynchronous Receiver Transmitter (UART)• Overview

• Hardware Interface

• Software Programming

• Technical Details• Chapter 12 of TI_Stellaris_LM3S1968.pdf

• Chapter 28 of TI_Stellaris_DriverLib.pdf

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Communicate Between Processors

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Host RxData

Host Tx

•Asynchronous -- Receiver does not know when data will arrive

•Protocol -- agreement between transmitter and receiver on the format of the data


Common Means of Communications

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• Serial -- one bit at a time• UARTs• USB• Ethernet• SSI -- Synchronous Serial Interface• I2C• CAN -- Component Area Network• PCIe -- PCI Express

• Parallel• Multiple Buses• HDMI• APB -- Advanced Peripheral Bus• DDR -- DRAM/Processor Bus


Common Protocols -- Asynchronous• Tx and Rx do not share common clock

• Receiver does not “know” when data will arrive• Start of transmission indication

• UART, Ethernet, CAN

• Receiver selection

• Parallel bus, I2C, SPI

• Clocks at Transmitter and Receiver can be (slightly) different• Tx and Rx agree on nominal clock rate, e.g. 115,200 bps

• Account for clock differences (UART, CAN)

• Embed clock in signals (Ethernet)

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UART Serial

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StartProtocolBit Time

SampleTime


Common Protocols -- Synchronous• Transmitter and Receiver share a common clock

• Start of transmission synchronized to common clock

• Data transmission synchronized to common clock

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0 0 1 0 0 1

E.g. Manchester Encoding (Ethernet)

1 0

31X

1 1

Ethernet Preamble -- 64 bits


Link Protocols• Single Protocol Data Unit (PDU)

• UART, I2C, SPI

• Short Protocol Data Units (PDUs)• CAN (1-8 Bytes)

• Long Protocol Data Units (PDUs)• USB, Ethernet, PCIe, HDMI

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Focus on UARTs• Functions

• Start of transmission

• Transmission of data

• Error detection

• End of transmission

• Parameters• Bit Rate (BAUD Rate)

• Number of bits (5-8)

• Parity (Even, Odd, None)

• Stop bits (1-2)

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Transmitting ASCII ‘e’

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• ASCII ‘e’ is 0x65

• Even Parity, total number of ‘1’ bits is even

• LSB transmitted first

• 1 Stop Bit

I St 1 0 1 0 0 1 1 0 0 Sp I


Transmitting ASCII ‘e’

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• Bit duration (time)

• Number of bits

• Parity

• Number of Stop bits

I St 1 0 1 0 0 1 1 0 0 Sp I

Parity

Stop Bits


Stellaris UART Features• A 16x12 bit receive FIFO and a 16x8 bit transmit FIFO.• Programmable baud rate generator.• Automatic generation and stripping of start, stop, and parity bits.• Line break generation and detection.• Programmable serial interface• 5, 6, 7, or 8 data bits• Even, odd, stick, or no parity bit generation and detection• 1 or 2 stop bit generation• Modem control/flow control• IrDA serial-IR (SIR) encoder/decoder.• DMA interface• 9-bit operation

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LM3S1968 Memory Map

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0x0000 0000

0x400F EFFF

0x4000 0000

0x2000 FFFF

0x0003 FFFF

0x2000 0000SRAM

Flash

Peripherals

64 KB

256 KB•Programs•Constants•Interrupt Vectors

•Variables•Stack

Base Addresses:

■ UART0: 0x4000.C000■ UART1: 0x4000.D000■ UART2: 0x4000.E000

Base Addr in: inc/hw_memmap.h


uartstdio.c include files

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#include <stdarg.h>#include "inc/hw_ints.h"#include "inc/hw_memmap.h"#include "inc/hw_types.h"#include "inc/hw_uart.h"#include "driverlib/debug.h"#include "driverlib/interrupt.h"#include "driverlib/rom.h"#include "driverlib/rom_map.h"#include "driverlib/sysctl.h"#include "driverlib/uart.h"#include "utils/uartstdio.h"

Defines UART Base Addr

Defines UART Offset Addr

Defines DriverLib UART Symbols


UART Block Diagram

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Ctrl/Status

Data

Bit Rate

Tx Data

Rx Data

SignalProc.


UART Register Map

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Offsets defined in: inc/hw_uart.h


Example Control Register (1)

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API Functions

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Initialize the UART with UARTStdio

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//*****************************************************************************//// Define the UARTStdio initization subroutine. Initialize the UART_0 on// PortA<1..0>.////*****************************************************************************

extern uint32_t UART_Initialization() {

if ( UARTStdioInitFlag == 0 ) {

// // Ensure the processor is initialized. // Processor_Initialization();

// // Enable UART0, to be used as a serial console. // SysCtlPeripheralEnable( SYSCTL_PERIPH_GPIOA ); SysCtlPeripheralEnable( SYSCTL_PERIPH_UART0 );

GPIOPinConfigure( GPIO_PA0_U0RX ); GPIOPinConfigure( GPIO_PA1_U0TX ); GPIOPinTypeUART( GPIO_PORTA_BASE, GPIO_PIN_0 | GPIO_PIN_1 );


Initialize the UART with UARTStdio

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UARTClockSourceSet( UART0_BASE, UART_CLOCK_SYSTEM );

// // Initialize UARTStdio // UARTStdioConfig( 0, 115200, g_ulSystemClock );

UARTStdioInitFlag = 1; // Set flag indicating initialization complete. }

return( 1 );}


uartstdio.c -- UARTprintf(const char *pcString, ...)

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//*****************************************************************************////! A simple UART based printf function supporting \%c, \%d, \%p, \%s, \%u,//! \%x, and \%X.//!//! \param pcString is the format string.//! \param ... are the optional arguments, which depend on the contents of the//! format string.//!//! This function is very similar to the C library <tt>fprintf()</tt> function.//! All of its output will be sent to the UART. Only the following formatting//! characters are supported://!//! – \%c to print a character//! – \%d to print a decimal value//! – \%s to print a string//! – \%u to print an unsigned decimal value//! – \%x to print a hexadecimal value using lower case letters//! – \%X to print a hexadecimal value using lower case letters (not upper case//! letters as would typically be used)//! – \%p to print a pointer as a hexadecimal value//! – \%\% to print out a \% character//!//! For \%s, \%d, \%u, \%p, \%x, and \%X, an optional number may reside//! between the \% and the format character, which specifies the minimum number//! of characters to use for that value; if preceded by a 0 then the extra//! characters will be filled with zeros instead of spaces. For example,//! ``\%8d'' will use eight characters to print the decimal value with spaces//! added to reach eight; ``\%08d'' will use eight characters as well but will//! add zeroes instead of spaces.//!//! The type of the arguments after \e pcString must match the requirements of//! the format string. For example, if an integer was passed where a string//! was expected, an error of some kind will most likely occur.//!//! \return None.////*****************************************************************************

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Universal Asynchronous Receiver Transmitter UARTittc.ku.edu/~gminden/Embedded_Systems/Lectures/EECS_388_UART_B40211.pdf• Focus on Universal Asynchronous Receiver Transmitter (UART)