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EEE527Embedded Systems
Lecture 9:Chapter 9: UARTs (version 2 – 25/11/13 changed slides 11-17, added
new at end)
Ian McCrum Room 5B18, Tel: 90 366364 voice mail on 6th ringEmail: IJ.McCrum@Ulster.ac.uk Web site: http://www.eej.ulst.ac.uk
"Adapted from the text “Programming 32-bit Microcontrollers in C –Exploring the PIC32 , © 2008.” Lucio di Jasio
www.eej.ulster.ac.uk/~ian/modules/EEE527/files
From : Di Jasio - Programming 32-bit Microcontrollers in C with additions by Ian McCrum
Simplified UART block diagramSimplified UART block diagram
figure 19-1 (DS61143)
From : Di Jasio - Programming 32-bit Microcontrollers in C with additions by Ian McCrum
Baud Rate settingBaud Rate setting
In our case this translates to the following expression:U2BREG = (25,000,000 / 4 / 115,200) -1 = 53.25 To decide how to best round out the result, use the reverse formula to calculate the actual baud-rate and determine the percentage error:Error = ((Fpb / 4 / (U2BREG + 1)) – baud rate) / baud rate %
With a value of 53 -> 115,740 Baud with an error of just 0.47%, With a value of 54 -> 113,636 baud, 1.82% error, Both are within the acceptable tolerance range for a standard RS232 port (+/- 2%) .We can therefore define the constant BRATE as:
#define BRATE 53 // 115,200 Bd (BREGH=1)
From : Di Jasio - Programming 32-bit Microcontrollers in C with additions by Ian McCrum
Use Excel to Calculate valuesUse Excel to Calculate values
SYS_CLK PB divisor PBCLK Baudrate UxBRG Actual Baudrate Error Actual Baudrate Error =PBCLK/(4*baud) -1' Round Down for Rounded down Round up for Rounded up =PBCLK/(4*(UxBRG+1))'
Number Number Formula Number Formula Formula Formula Formula Formula Formula Formula e.g e.g e.g e.g e.g e.g e.g e.g C8=A8/B8 E8=C8/(4*D8) - 1 =roundown(E8,0) G8=C8/((4*(F8+1)) (G8-D8)/D8 =roundup(E8,0) J8=C8/(4*(I8+1)) (G8-D8)/D8
50000000 2 25000000 115200 53.25347222 53 115740.7407 0.47% 54 113636.3636 -1.82%50000000 2 25000000 38400 161.7604167 161 38580.24691 0.47% 162 38343.55828 -0.61%50000000 2 25000000 19200 324.5208333 324 19230.76923 0.16% 325 19171.77914 -0.31%50000000 2 25000000 9600 650.0416667 650 9600.614439 0.01% 651 9585.889571 -0.15%50000000 2 25000000 1200 5207.333333 5207 1200.076805 0.01% 5208 1199.84642 -0.02%
See the File
EEE527_PIC32MX_BAUD_RATE_GENERATOR.xlsx
From : Di Jasio - Programming 32-bit Microcontrollers in C with additions by Ian McCrum
UxMODE registerUxMODE register
register 18-1 (DS61168E)
From : Di Jasio - Programming 32-bit Microcontrollers in C with additions by Ian McCrum
Important BITs of UxMODEImportant BITs of UxMODE
ON (bit 15) 1 is enabled, UARTx pins controlled by UEN<1:0> and UTXEN
SIDL (bit 13) only relevant in idle mode
IREN (bit 12) 0 = IrDA is disabled
RTSMD (bit 11) 1 = /UxRTS is in Simplex mode
UEN (bits 9-8) 00 = Use UxTX/RX, /UxCTS ,/UxRTS/BCLK just used by PORTx
WAKE (bit 7) only relevant in sleep mode
LPBACK (bit 6) 0 = loopback disabled
ABAUD (bit 5 ) 0 = Auto-Baud rate detection is disabled or completed.
RXINV (bit 4) 0 = UxRX idle state is a ‘1’ ( sent in RS232 as -12V!)
BRGH (bit 3) 1 = High-speed mode – 4x baud clock enabled. {0= x16}
PDSEL (bits2-1) 00 = 8 bit data, no parity {01=8E, 10=8O (odd), 11=9N }
STSEL (bit 0) 0 = 1 stop bit {1 = 2 stop bits}
- - - - - - - - - - - - - - - - 1ux0 1u00 x000 1000 = 0x8888
From : Di Jasio - Programming 32-bit Microcontrollers in C with additions by Ian McCrum
UxSTA registerUxSTA register
register 18-2 (DS61168E)
From : Di Jasio - Programming 32-bit Microcontrollers in C with additions by Ian McCrum
ADM_EN (bit 24) 0 = no automatic address detect
ADDR<7:0> (bits 23-16) only matter when bit above is set
UTXISEL<1:0> (bits15-14) 01 = raise interrupt when all chars transmitted
UTXINV (bit 13) 0 = UxTX idle state is ‘1’ (if not in IrDA mode)
URXEN (bit 12) 1 = UARTx receiver is enabled
UTXBRK (bit 11) 0 = send no break {1=send start, 12 ‘0’ and stop}
UTXEN (bit 10) 1 = UARTx transmitter is enabled
UTXBF (bit 9) 1 = Transmit buffer is full {0 = room for at least 1 char}
TRMT (bit 8) 0 = Transmit Shift Register is not empty, tx in progress
URXISEL<1:0> (bit 7-6) 00 = Int flag is asserted while rx buffer not empty
ADDEN (bit 5) 0 = Address detect mode disabled
RIDLE (bit 4) 0 = Data is being received {1=receiver is idle}
PERR (bit 3) 1 = Parity error detected for current character
FERR (bit 2) 1 = Framing error detected for current character
OERR (bit 1) 1 = Receiver buffer overrun. Can only be cleared in s/w
URXDA (bit 0) 1 = Receive buffer data available, at least one char.
Important BITs of UxSTAImportant BITs of UxSTA
e.g. U2STA = 0x1400;
From : Di Jasio - Programming 32-bit Microcontrollers in C with additions by Ian McCrum
In the DP32 it is simpler to use UART2 – it shares pins In the DP32 it is simpler to use UART2 – it shares pins with the I2C pins going to JP4 & 5with the I2C pins going to JP4 & 5
Use UART2 and PPS -> U2TX/RPB9U2RX/RPB8 NBRemove jumpers JP4 & 5And do not insert IC2C, the 8 pin chip
From : Di Jasio - Programming 32-bit Microcontrollers in C with additions by Ian McCrum
You need to program which pins go where – look up Peripheral Pin Select (PPS) in the datasheet. Also the PPS LOCK and UNLOCK sequences.
From : Di Jasio - Programming 32-bit Microcontrollers in C with additions by Ian McCrum
Next 4 slides give working code; create a project called UART_1 and either
wire RB8 and RB9 to a USB TTL 3.3V Usart,
or a PICKIT2
or to another DP32 - but wire
RB8_board1 to RB9_board2 And
RB9_board2 to RB8_board2
(on the PC run PUTTY or PICKIT2 v2.6.1 (NOT PICKIT3 s/w!)
From : Di Jasio - Programming 32-bit Microcontrollers in C with additions by Ian McCrum
Code to demo serial i/oCode to demo serial i/o
Modified from http://umassamherstm5.org/tech-tutorials/pic32-tutorials/pic32mx220-tutorials/uart-to-serial-terminal
From : Di Jasio - Programming 32-bit Microcontrollers in C with additions by Ian McCrum
NB remove JP4 and JP5 (rotate 180 degrees)
Modified from http://umassamherstm5.org/tech-tutorials/pic32-tutorials/pic32mx220-tutorials/uart-to-serial-terminal
From : Di Jasio - Programming 32-bit Microcontrollers in C with additions by Ian McCrum
Modified from http://umassamherstm5.org/tech-tutorials/pic32-tutorials/pic32mx220-tutorials/uart-to-serial-terminal
From : Di Jasio - Programming 32-bit Microcontrollers in C with additions by Ian McCrum
Modified from http://umassamherstm5.org/tech-tutorials/pic32-tutorials/pic32mx220-tutorials/uart-to-serial-terminal
From : Di Jasio - Programming 32-bit Microcontrollers in C with additions by Ian McCrum
ExercisesExercises Send data every second to another DP32 and
display it there. (The sending board can be called DP32_1 and the receiver DP32_2)
Send data only when a pushbutton on DP32_1 is pressed.
Send data only when the receiving end says it is ready. (hint wire another wire from a spare i/o line from Dp32_2 to DP32_1.
Use LEDs to show various things
From : Di Jasio - Programming 32-bit Microcontrollers in C with additions by Ian McCrum
Timer delaysTimer delays These can use an interrupt – see notes for a 1 second ISR using a
flag variable that main polls. A simple delay is a “blocking” wait. E.g
#define DELAY 39062 // assuming 40Mhz clock
…
// In main near start
T1CON = 0x8030; // prescale 256:1, 40Mhz=25nSec and 25/256=> 6.4usec
Then for a delay use in your code the following two lines (or put in a function)
TMR1=0;PR1=0xFFFF; // Note the 39062 gives a slight inaccuracy.
while(TMR1 < DELAY){;}// wait here for 39062 * 6.4uSecs
// you arrive here after a quarter second…(reasonably accurate…)
From : Di Jasio - Programming 32-bit Microcontrollers in C with additions by Ian McCrum
You can also use the plib library (this code needs modified for the DP32! Do not use as is
PPSUnLock; // Allow PIN Mapping PPSOutput(4, RPB10, U2TX); // MAP Tx to PB10 PPSInput (2, U2RX, RPB11); // MAP Rx to PB11 PPSLock; // Prevent Accidental Mapping
// Configure UART2
UARTConfigure(UART2, UART_ENABLE_PINS_TX_RX_ONLY);
UARTSetLineControl(UART2 ,UART_DATA_SIZE_8_BITS | UART_PARITY_NONE | UART_STOP_BITS_1);
UARTSetDataRate(UART2, GetPeripheralClock(), BaudRate); UARTEnable(UART2 ,UART_ENABLE_FLAGS(UART_PERIPHERAL | UART_RX | UART_TX));
This code is explained athttp://www.eevblog.com/forum/microcontrollers/pic32mx-quickstart/15/
From : Di Jasio - Programming 32-bit Microcontrollers in C with additions by Ian McCrum
Print a message Function using plibPrint a message Function using plib
void Serial_print(char *buffer){ while(*buffer != (char)0) { while(!UARTTransmitterIsReady(UART2)); UARTSendDataByte(UART2, *buffer++); } while(!UARTTransmissionHasCompleted(UART2)); UARTSendDataByte(UART2, '\r'); UARTSendDataByte(UART2, '\n'); }
This code is explained athttp://www.eevblog.com/forum/microcontrollers/pic32mx-quickstart/15/
From : Di Jasio - Programming 32-bit Microcontrollers in C with additions by Ian McCrum
Sending and Receiving Data using Sending and Receiving Data using handshake lines – CTS and RTS handshake lines – CTS and RTS
(manually)(manually)int putU2( int c){ while ( CTS); // wait for !CTS, clear to send while ( U2STAbits.UTXBF); // wait while Tx buffer full U2TXREG = c; return c;} // putU2
char getU2( void){ RTS = 0; // assert Request To Send !RTS while ( !U2STAbits.URXDA); // wait for a new char to arrive RTS = 1; return U2RXREG; // read char from receive buffer}// getU2
Could be worth adding the lines, just before the return c;
while( !U2STAbits.TRMT);
From : Di Jasio - Programming 32-bit Microcontrollers in C with additions by Ian McCrum
Serial terminal programs on the PCSerial terminal programs on the PC Hyperterminal – pre windows 7 in all versions RealTerm - most excellent, doesn’t work W8 Putty – usually used for network login MPIDE has a good serial monitor
Use USB to serial convertors if the PC has no serial ports PICKit 2 can do USB to Serial conversion (but not yet
working on the PICKit 3) Select 3.3V before plugging in. You can buy USB to Serial convertors, either full RS232 or
just TTL UART. Be careful you do not damage the board! You want 3.3Volts maximum Also several I have used output on pins labelled RCV and input on TX – I had to use a scope to check!
From : Di Jasio - Programming 32-bit Microcontrollers in C with additions by Ian McCrum
HyperTerminal Setup (windows XP only)HyperTerminal Setup (windows XP only)
From : Di Jasio - Programming 32-bit Microcontrollers in C with additions by Ian McCrum
RealTerm runs on XP and windows 7 (but not 8)RealTerm runs on XP and windows 7 (but not 8)
From : Di Jasio - Programming 32-bit Microcontrollers in C with additions by Ian McCrum
PUTTY can perform serial PUTTY can perform serial terminal functionsterminal functions
When programming the PIC32 and with the UART output connected to Putty many random characters are sent from the PIC to PUTTY.
If the handshaking is left at the default XON/XOFF then PUTTY may receive a XOFF (control-S) from the PIC and you have to quit and restart PUTTY after every programming
Alternatively select the correct handshaking protocol. Such as clicking on the Serial menu option and selecting “NONE” or “HARDWARE RTS/CTS”
Use the Device manager to check the COM port of the USB-TTL adaptor
Ensure the Speed is correct
From : Di Jasio - Programming 32-bit Microcontrollers in C with additions by Ian McCrum
PICKit2 comes with UART Software – PICKit2 comes with UART Software – NB NOT the PICKit3 (yet)NB NOT the PICKit3 (yet)
Wire up the PICKit2 asPICKit Pin 1 - No ConnectionPICKit Pin 2 - 3V3PICKit Pin 3 - GNDPICKit Pin 4 – DP32 Pin 7 (Tx) RB14PICKit Pin 5 - DP32 Pin 10 (Rx) RA1PICKit Pin 6 - No Connection
Start the PICKit 2 application and select Tools-->UART Tool
From : Di Jasio - Programming 32-bit Microcontrollers in C with additions by Ian McCrum
The PICKit2 has other uses;The PICKit2 has other uses;You can also use the Logic Analyzer Mode.
Click 'Exit UART Tool' and start the Logic ToolSelect 'Analyser' if it is not on by default.Set the Sample rate to 100 Khz and the Trigger to Ch1 \ (falling edge)Click Capture and, When your code sends 'Hello World!' you should see…
From : Di Jasio - Programming 32-bit Microcontrollers in C with additions by Ian McCrum
Tips and TricksTips and TricksTo re-direct the output stream of the standard C library (stdio.h) functions such as printf() to a UART:
Define the function: _mon_putc() Note that a “weak” definition is already provided in the library to send the default
output stream (stdout) to UART2 (convenient for all Explorer16 users).
Similarly define: _mon_getc() A default “weak” version is already provided in the library as well, connecting
UART2 receiver to the input stream (stdin). Weak means that the compiler won’t complain when you define a new function
with the same name, it will simply replace it with the new one you provide.
NOTEYou are responsible for the UART initialization! Before the first call to any stdio function (printf()…) make sure the UART2 is enabled and the baud rate is set correctly.
From : Di Jasio - Programming 32-bit Microcontrollers in C with additions by Ian McCrum
Code for serial i/o, allowing printf & putsCode for serial i/o, allowing printf & puts
By adding a function called _mon_putc() the linker will use it for calls to printf() and puts()
From : Di Jasio - Programming 32-bit Microcontrollers in C with additions by Ian McCrum
Once you define _mon_putc() any call to Once you define _mon_putc() any call to printf or puts will just workprintf or puts will just work
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