LPC1768 UART programing
Contents
1. 1 Linux man page Available at http linux die net man l minicom Last visited December 2010 3 NXP Semiconductors UM10360 LPCI7xx user manual Available at http ics nxp com support documents microcontrollers pdfluser manual pcl7xx pdf Last visited December 2010 122. Q We can also setting the minicom on the fly when running by press Ctrl A and then O This will bring the minicom s main configuration interface LPC1768 UART programming v 1 22 December 2010 Ill UART programming To do the UART programming we basically need to do two things The first thing is set up the UART i e enable it setting parameters such as speed number of data bits parity bit or not and number of stop bit The second thing is providing an interrupt handler function to manage it i e specify what to do when there is data to receive when there is no data to transmit and when there are errors and register this function with the system so that the system knows which function to call when the UART associated events occur The register is quite simple We just need to put a pointer to that function in the defined place for UART in the system interrupt vector However in our case an interrupt vector with dummy interrupt handlers for most cases have been provided so what we need to do is that figure out the name of the interrupt handler function which can be one of UARTO IRQHandler UARTI IRQHandler UART2 IRQHandler or UART3 IRQHandler and use the same name for our interrupt handler function Our defined function will override the dummy function For the list of all provided dummy function see the file LPC1768 handlers c 111 1 Setup the UART To setup the UART we need to do the following things First we need to choo
3. first character in the buffer WA uint8 tuart rx buf read byte uart buffer type buff x Read number of bytes from the receiving buffer The characters will be deleted from the receiving buffer param buff a pointer to the data structer that contain the transmitting and receiving buffer param result a pointer to a place to contain the results param number of byte the number of bytes to read return the number of character that actually read H uint8 t uart_rx_buf_read uart_buffer_type buff uint8_t result uint8 t number of byte x Write byte ch to the receiving buffer param ch byte to write to the buffer param buff a pointer to the data structer that contain the transmitting and receiving buffer return 0 if sucessful 1 if the buffer is full 11 LPC1768 UART programming v 1 22 December 2010 Ka uint8 t uart rx_buf write byte uint8 t ch uart buffer type buff Write string to the receiving buffer param charBuff string to write to the buffer param buff a pointer to the data structer that contain the transmitting and receiving buffer return 0 if sucessful 1 if the buffer is full uint8 tuart rx buf write char charBuf uart_buffer_type buff Reference 1 Universal asynchronous receiver transmitter Available at http en wikipedia org wiki Universal asynchronous receiver transmitter Last visited December 2010 2 minicom
4. is full Underrun error it signals that the UART transmitter buffer is empty Framing error it means that the start and stop bits are not valid e Parity error it is set when the received parity bit does not match the calculated one Break interrupt it is held when the received serial line is in the spacing state all zeros for more than one full character transmission 1 3 UART Pin Connection To send and receive data the two UART ports must be connected by a serial link To connect two UARTS we connect the transmitter pin of this UART to the receiver pin of the other pin and vice versa The ground pin of the two UARTS also need to be connected The connection diagram of the serial link is showed in figure 2 LPCI768 UART programming v 1 22 December 2010 Figure 2 UART pin connection Il Minicom A very useful application when programming with UART is the serial communication application It allows us to send the data to the UART and receive the data back which plays a very important role in debugging A popular serial communication program is minicom In Ubuntu minicom can be installed using the following command sudo apt get install minicom To use minicom we need to first configure it by using the below command sudo minicom s The following interface is displayed Figure 3 Minicom configuration interface First we need to setup the serial port by choosing Serial port setup LPC1768 UART progra
5. the UART in bytes and the UART then transmits them as sequential individual bits At the receiver side the sequential bits received from the serial link are assembled into bytes and placed into the receiver register waiting for reading To perform the function of converting between serial and parallel form shift registers are used in the UART The UART is of the asynchronous transmission type which means that there is no clock signal between the two communicated parties instead the communication configuration speed number of data bits parity bit or not number of stop bits is agreed in advance and special bits for the synchronization are transmitted The character framing of it is showed in figure 1 Figure 1 UART character framing reproduced from 1 Before the transmission of a data word a special bit the start bit is transmitted to inform the receiver and also to synchronize the receiver s clock The difference between the two clocks should not exceed 10 percent during the data bit transmissions After that the data bits are sent from the least significant bit to the most significant bit And then a parity bit which is used for the error checking may be sent and finally one or more stop bits which signal the end of the word is sent 1 2 Communication Error During the UART communication session some of the following errors may occur e Overrun error the error occurs when a new character arrives and the UART receiver buffer
6. LPC1768 UART programming v 1 22 December 2010 MInNs MINIMAL NETWORK ELEMENT III LPC1768 UART programing Team Members Bikash Shakya 15 ECTS Huy Nguyen 15 ECTS Markku Antikainen 24 ECTS Mudassir Asif 24 ECTS Muhammad Ziad 24 ECTS Naresh Kumar Khatri 24 ECTS Siddharth Sharma 15 ECTS Version 1 0 Huy Nguyen 22 December 2010 Coaches Bernt Sundstr m Hans Eriksson Robert Olsson Champion Bj rn Pehrson LPC1768 UART programming v 1 22 December 2010 History 22 December 2010 1 Created LPC1768 UART programming v 1 22 December 2010 Table of Contents EAN v O O O O 4 L1 aa yoye La eni c 4 1 2 Communication Error soap epe eege 4 1 3 UART Pin Conus aa wawi und m Miren ipia tra M m eM EI pe Eaka md MEE 5 TUBIS nate ac M 3 ME UART PESTO ATE TE OO T S LITERE 8 WI Setup the LAB E o pte o an ande d ted deal a omnes denn M beken 8 II 2 Writing the interrupt handler TiC HO ege 9 EV Proj cts UART Propral EE 9 IVA Data SUCUT E 9 1y 2 Facility H 10 EEN 12 LPC1768 UART programming v 1 22 December 2010 I UART 1 1 Introduction The UART universal asynchronous receiver transmitter is mainly used for the communication between computer systems The communication can be in full duplex mode or half duplex mode At the sender side the data is given to
7. evice which is connected to the blue board to Serial Device option To change the device type A then LPCI768 UART programming v 1 22 December 2010 type the device for example dev ttyUSB1 and press Enter Next we need to configure the transmission speed the number of data bit parity and the number of stop bits We do it by type E then type the character corresponding to the options we want Type Enter when finish Figure 5 Communication parameter setting interface Then type F to change Hardware flow control to no And press Enter to exit to the main setting interface After setting we need to save it so we do not to do the setup next time Choose Save setup as dfl to save this setting as the default setting Choose Save setup as to save the setting to another file Now choose Exit from Minicom to exit it and then start it again with the following command minicom o The o option is used to disable the initialization which can bring undesirable result in our case With this command minicom will use the setting from the default configuration file To use a difference configuration file specify the filename as argument when start minicom minicom o configuration_file We can also override any setting in the configuration file using the command line options For the list of available options please see the Linux minicom man page 2 or minicom s readme file To quit minicom press Ctrl A and then press
8. f each function please consult the function code in the uart c write data to the transmitting fifo change this function for different behaviours param buff a pointer to the data structer that contain the transmitting and receiving buffer param number of byte the number of byte to send H void uart send uart buffer type buff uint8 t number of byte uint8 t uart num Write string to the transmitting buffer param charBuff string to write to the buffer param buff a pointer to the data structer that contain the transmitting and receiving buffer return 0 if sucessful 1 if the buffer is full WA 10 LPC1768 UART programming v 1 22 December 2010 uint8 t uart tx buf write char charBuf uart buffer type buff x Write byte ch to the transmitting buffer param ch byte to write to the buffer param buff a pointer to the data structer that contain the transmitting and receiving buffer return 0 if sucessful 1 if the buffer is full WA uint8 t uart_tx_buf write byte uint8 t ch uart buffer type buff x Read byte from the receiving buffer The character will be deleted from the receiving buffer param buff a pointer to the data structer that contain the transmitting and receiving buffer return 0 if no character So in order to use the function may be should check the length of the receiving buffer first in case the buffer can contains 0 T the
9. mming v 1 22 December 2010 Figure 4 Minicom serial port setup interface In Serial Port Setup we first start with specifying the port for serial communication With our programming board using the dmesg command you can see something like this 11149 865325 fidi sio 2 1 1 0 FTDI USB Serial Device converter detected 11149 865413 usb 2 1 Detected FT2232C 11149 865415 usb 2 1 Number of endpoints 2 11149 865416 usb 2 1 Endpoint 1 MaxPacketSize 64 11149 865418 usb 2 1 Endpoint 2 MaxPacketSize 64 11149 865419 usb 2 1 Setting MaxPacketSize 64 11149 871488 usb 2 1 FTDI USB Serial Device converter now attached to tty USBO 11149 871498 fidi sio 2 1 1 1 FTDI USB Serial Device converter detected 11149 872001 usb 2 1 Detected FT2232C 11149 872001 usb 2 1 Number of endpoints 2 11149 872001 usb 2 1 Endpoint 1 MaxPacketSize 64 11149 872001 usb 2 1 Endpoint 2 MaxPacketSize 64 11149 872001 usb 2 1 Setting MaxPacketSize 64 11149 878268 usb 2 1 FTDI USB Serial Device converter now attached to ttvUSB1 11149 878450 usbcore registered new interface driver fidi sio 11149 878452 fidi sio v1 6 0 USB FTDI Serial Converters Driver In the above message the first FTDI USB Serial Device converter one which is now attached to ttvUSBO is the serial device connected to the programmer itself The second one which is now attached to ttyUSBI is the device connected to the blue board We need to specify the d
10. nterrupt handler is its name which must be the same as what in the LPCI768 handlers c and to remember to clear the corresponding interrupt flag if it does not clear automatically A good practice in the development phase is to use a led to signal when there is an interrupt The event which causes the interrupt can be identified using the Interrupt Identification Register IIR together with the Line Status Register LSR The received data can be read from the Receiver Buffer Register RBR To transmit data just write it to the Transmit Holding Register THR Note that in order to access these two registers the DLAB bit of the LCR also need to be set to 0 For the implementation of the UART interrupt handler please see the UARTO IRQHandler of the file uart c IV Project s UART Program Beside the interrupt handler and the initialized function the project UART code also contains a data structure along with its managed facility functions for the ease of working with UART IV 1 Data structure The data structure which is used in our UART is showed below typedef struct uint8 trx buf UART BUFFER SIZE receive buffer uint8 t tx buf UART BUFFER SIZE transmit buffer volatile uintl6 rr start index the index of starting index for received byte volatile uint16 trx len the number of bytes in the receiving buffer volatile uint16 ttx start index the index of starting byte for transmitting volatile uintl16 ttx len the numbe
11. r of bytes in the transmitting buffer j uart buffer type This structure defines two buffer arrays for receiving and transmitting data with necessary information to manage them The size of both arrays is 256 bytes and can be changed via the UART BUFFER SIZE The buffer is a round buffer meaning that the data will be store continuously from index the beginning to the end of the array and then back to the beginning Each array has two parameters the start index and the len The start index tells us the array index of the data that has not been reading in case of receiving buffer or has not been transmitting in case of LPC1768 UART programming v 1 22 December 2010 transmitting buffer The len parameter indicates how many data left Start index Figure 6 UART array buffer When the UART receives data from the serial link it will read them from the receive FIFO and store them in the receiving buffer after the current unprocessed receiving data When system wants to transmit data using the UART the data will be first written to the transmitting buffer When the UART sees that its transmit FIFO is empty it will try to fill the transmit FIFO by reading from the transmitting buffer For more detail please consult the UART interrupt handler function in the uart c IV 2 Facility functions The facility functions are mostly associated with handling the buffer arrays Their definitions and short descriptions are listed below For detail o
12. se the UART port we want to use figure out its pins for receiving and transmitting and set up the pin for UART using the pins control register Because the LPC1768 have four UART ports from port 0 to port 3 and associating with each port is a pair of transmitter and receiver pins so we need to find out which are the pins for our desire port Beside that since each pin in the LPC1768 may have several different functions and different modes we also have to configure the pin so that they are suitable to be used for the UART Second we need to enable the power for our port via the PCONP register because the LPC1768 allows us to disable power to unused peripherals for power saving Our next step is setting the clock This is important since it will relate to our UART speed calculation later The clock for UART is derived from the CPU clock CCLK so we need to know the speed of the CPU clock before deciding the UART clock value The CPU clock can be setting using the Clock Source Select register CLKSRCSEL and Phase Locked Loop 0 PLLO In our case the internal clock of the LPC1768 which has the speed of 4Mhz is used for the CPU The values of the UART clock can be CCLK CCLK 2 CCLK 4 and CCLK 8 The desirable value can be choose by writing the appropriate value to the Peripheral clock selection register PCLKSELO and PCLKSEL 1 Now it s time to configure the UART speed the baud rate The baud rate is configured by writing appropriate
13. values the the ports Divisor Latch LSB register DLL Divisor Latch MSB register DLM and Fractional Divider Register FDR For detail on how to calculate these values please refer to section 14 4 12 of the LPC1768 user manual 3 Note that in order to be able to access these registers we need first to set the DLAB bit of the Line Control Register LCR to 1 Next we will choose the format of the character when transmitting the number of data bits parity and the number of stop bits using the Line Control Register LCR We also choose to use the FIFO buffer 16 bytes or not via the FIFO Control Register FCR Our last step is to decide which UART events to be enabled i e which events for this UART port will cause the interrupt handler function to be called and enable the UART interrupt in the NVIC LPC1768 UART programming v 1 22 December 2010 register so the events will be reported to the CPU which in turn will call the interrupt handler function The types of UART events can be seen and enabled from the Interrupt Enable Register IER Also note that in order to change the IER we have to set the DLAB bit of the LCR to 0 For detail of how these tasks are implemented please see the UART init function of the uart c IIl 2 Writing the interrupt handler function The interrupt handler is called when the events corresponding to what are enabled in the UART port IER register The only things we need to concern when writing the i
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