MikroElektronika PIC Microcontrollers PIC18 Manual de usuario descargar pdf (Pagina 33)

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The COLLECTOR processor reads the temperature, formats it, and sends to the

DISPLAY processor over the CAN bus

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The DISPLAY processor reads the temperature from the CAN bus and then

displays it on the LCD

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This process is repeated every second

DISPLAY Program

Figure 9.17 shows the program listing of the DISPLAY program, called DISPLAY.C.

At the beginning of the program PORTC pins are configured as outputs, RB3 is

configured as input (CANRX), and RB2 is configured as output (CANTX). In this

project the CAN bus bit rate is selected as 100Kb/s. With a microcontroller clock

frequency of 8MHz, the Baud Rate Calculator program (see Figure 9.14) is used to

calculate the timing parameters as:

SJW ¼ 1

BRP ¼ 1

Phase_Seg1 ¼ 6

Phase_Seg2 ¼ 7

Prop_Seg ¼ 6

The mikroC CAN bus function CANInitialize is used to initialize the CAN module. The

timing parameters and the initialization flag are specified as arguments in this function.

The initialization flag is made up from the bitwise AND of:

init_flag ¼ CAN_CONFIG_SAMPLE_THRICE &

CAN_CONFIG_PHSEG2_PRG_ON &

CAN_CONFIG_STD_MSG &

CAN_CONFIG_DBL_BUFFER_ON &

CAN_CONFIG_VALID_XTD_MSG &

CAN_CONFIG_LINE_FILTER_OFF;

Where sampling the bus three times is specified, the standard identifier is specified,

double buffering is turned on, and the line filter is turned off.

Then the operation mode is set to CONFIG and the filter masks and filter values are specified.

Bothmask1andmask2aresettoall1’s(1 is a shorthand way of writing hexadecimal

FFFFFFFF, i.e., setting all mask bits to 1’s) so that all filter bits match up with incoming data.

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507Advanced PIC18 Projects—CAN Bus Projects

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MikroElektronika PIC Microcontrollers PIC18 Manual de usuario Pagina 33