elct 912: advanced embedded systems - …eee.guc.edu.eg/courses/electronics/advanced embedded...

ELCT 912:

Advanced Embedded

Systems

Lecture 10: Applications for Programming PIC18 in C

Dr. Mohamed Abd El Ghany,

Department of Electronics and Electrical Engineering

Programming the PIC18 to transfer

data serially

2 Dr. Mohamed Abd el Ghany

Department of Electronics and Electrical Engineering ELCT 912:

Advanced embedded Systems

Winter 2011

1. The TXSTA register is loaded with the value 20H,

indicating asynchronous mode with 8-bit data frame, low

baud rate, and transmit enabled.

2. Make TX pin of PORTC (RC6) an output for data to come

out of the PIC

3. The SPBRG is loaded with value to set the baud rate for

serial data transfer

4. SPEN bit in the RCSTA register is set HIGH to enable the

serial port of PIC18

5. The character byte to be transmitted serially is written into

the TXREG register.

6. Monitor the TXIF bit of the PIR1 register to make sure

UART is ready for next byte

7. To transfer the next character, go to step 5

Programming the PIC18 to transfer data serially




Winter 2011

Write a C program for the PIC18 to transfer the letter „G‟ serially at

9600 baud, continuously. Use 8-bit data and 1 stop bit. Assume XTAL =

10 MHz.

Programming the PIC18 to transfer data serially




Winter 2011

Write a PIC18 C program to transfer the message “YES” serially at

9600 baud, 8-bit data, and 1 stop bit. Do this continuously.

Programming the PIC18 to receive

data serially




Winter 2011

1. The RCSTA register is loaded with the value 90H, to

enable the continuous receive in addition to the 8-bit data

size option

2. The TXSTA register is loaded with the value 00H to

choose the low baud rate option.

3. SPBRG is loaded with a value to set the baud rate

4. Make the RX pin of PORTC (RC7) an input for data to

come into the PIC18.

5. The RCIF flag bit of the PIR1 register is monitored for a

HIGH to see if an entire character has been received yet.

6. When RCIF is raised, the RCREG register has the byte.

Its contents are moved into a safe place

7. To receive the next character, go to Step5

Programming the PIC18 to receive data serially




Winter 2011

Program the PIC18 in C to receive bytes of data serially and put them

on PORTB. Set the baud rate at 9600, 8-bit data, and 1 stop bit.

Example




Winter 2011

Write an C18 program to send two different strings to the serial port.

Assuming that SW is connected to pin PORTB.5, monitor its status and

make a decision as follows:

SW = 0; send your first name

SW = 1; send your last name

Assuming XTAL =10 MHz, baud rate of 9600, and 8-bit data

Part 1

Example




Winter 2011

Part 2

Baud rates for BRGH =1




Winter 2011

Note : for Fosc = 10 MHz, we have SPBRG = (625000/ Baud Rate) – 1

SPBRG Values for Various Baud

Rates (XTAL = 10 MHz)




Winter 2011

Baud rates error calculation




Winter 2011

For example, with the XTAL = 10 MHz and BRGH =0, we have the

following for the 9600 baud rate:

SPBRG value = (156250/9600)-1= 16.27 – 1= 15.27 =15

Error = (15.27– 15)/16 = 1.7%

Example




Winter 2011

Write a PIC18 C program to send the two messages “Normal speed”

and “High Speed” to the serial port. Assuming that SW is connected to

pin PORTB.0, monitor its status and set the baud rate as follows:

SW =0 9600 baud rate

SW =1 38400 baud rate

Assuming XTAL =10 MHz for both cases.

Part 1

Example




Winter 2011

Part 2

Programming Timer Interrupts




Winter 2011

Timer Interrupt Flag Bits and Associated Registers

INTCON Register with Timer0 Interrupt Enable and Interrupt Flag

Programming Timer Interrupts




Winter 2011

The Role of Timer Interrupt Enable Flag (TMRxIE)

The Difference Between the

RETURN and RETFIE Instructions




Winter 2011

Explain why we cannot use RETURN instead of RETFIE as the

last instruction of ISR

Both perform the same actions of popping off the top bytes of

the stack into the program counter and making the PIC18 return

to where it left off. However, RETFIE also performs the additional

task of clearing the GIE flag, indicating that the servicing of the

interrupt is over and the PIC18 now can accept a new interrupt. If

you use RETURN instead of RETFIE as the last instruction of

interrupt service routine, you simply block any new interrupt

after the first interrupt, because the GIE would indicate that the

interrupt is still being serviced.

Example




Winter 2011

Write a program to use Timer0 and Timer1 interrupts to generate

square waves on pins RB1 and RB7 respectively, while data is being

transferred from PORTC to PORTD

Part 1

Example




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Part 2

Example




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Part 3

Example




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Part 4

PIC18 interrupt Programming in C




Winter 2011

Notes:

The C18 compiler uses ”#pragma code” to place code

at a specific ROM address.

Because the C18 does not pace an ISR at the interrupt

vector table automatically, we must use assembly

language instruction GOTO at the interrupt vector to

transfer control to the ISR.

PIC18 interrupt Programming in C




Winter 2011

Now we redirect it from address location 00008 to another

program to find the source of the interrupt and finally to the

ISR. This is done with the help of the keyword „interrupt‟ as

follows:

Example




Winter 2011

Write a program to use Timer0 and Timer1 interrupts to generate

square waves on pins RB1 and RB7 respectively, while data is being

transferred from PORTC to PORTD ( C version)

Part 1

Example




Winter 2011

Part 2

Example




Winter 2011

Part 3

Example




Winter 2011

Part 4

elct 912: advanced embedded systems - …eee.guc.edu.eg/courses/electronics/advanced embedded...

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