Книга: Advanced PIC Microcontroller Projects in C

DISPLAY Program

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        = 1
BRP        = 1
Phase_Seg1 = 6
Phase_Seg2 = 7
Prop_Seg   = 6
/**********************************************************************
                   CAN BUS EXAMPLE - NODE: DISPLAY
                   ===============================
This is the DISPLAY node of the CAN bus example. In this project a PIC18F258
type microcontroller is used. An MCP2551 type CAN bus transceiver is used to
connect the microcontroller to the CAN bus. The microcontroller is operated
from an 8MHz crystal with an external reset button.
Pin CANRX and CANTX of the microcontroller are connected to pins RXD
and TXD of the transceiver chip respectively. Pins CANH and CANL of
the transceiver chip are connected to the CAN bus.
An LCD is connected to PORTC of the microcontroller. The ambient
temperature is read from another CAN node and is displayed on the LCD.
The LCD is connected to the microcontroller as follows:
Microcontroller LCD
     RC0        D4
     RC1        D5
     RC2        D6
     RC3        D7
     RC4        RS
     RC5        EN
CAN speed parameters are:
Microcontroller clock: 8MHz
CAN Bus bit rate:      100Kb/s
Sync_Seg:              1
Prop_Seg:              6
Phase_Seg1:            6
Phase_Seg2:            7
SJW:                   1
BRP:                   1
Sample point:          65%
Author: Dogan Ibrahim
Date:   October 2007
File:   DISPLAY.C
**********************************************************************/
void main() {
 unsigned char temperature, data[8];
 unsigned short init_flag, send_flag, dt, len, read_flag;
 char SJW, BRP, Phase_Seg1, Phase_Seg2, Prop_Seg, txt[4];
 long id, mask;
 TRISC = 0;    // PORTC are outputs (LCD)
 TRISB = 0x08; // RB2 is output, RB3 is input
 //
 // CAN BUS Parameters
 //
 SJW = 1;
 BRP = 1;
 Phase_Seg1 = 6;
 Phase_Seg2 = 7;
 Prop_Seg = 6;
 init_flag = 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;
 send_flag = CAN_TX_PRIORITY_0 &
  CAN_TX_XTD_FRAME &
  CAN_TX_NO_RTR_FRAME;
 read_flag = 0;
 //
 // Initialize CAN module
 //
 CANInitialize(SJW, BRP, Phase_Seg1, Phase_Seg2, Prop_Seg, init_flag);
 //
 // Set CAN CONFIG mode
 //
 CANSetOperationMode(CAN_MODE_CONFIG, 0xFF);
 mask = -1;
 //
 // Set all MASK1 bits to 1's
 //
 CANSetMask(CAN_MASK_B1, mask, CAN_CONFIG_XTD_MSG);
 //
 // Set all MASK2 bits to 1's
 //
 CANSetMask(CAN_MASK_B2, mask, CAN_CONFIG_XTD_MSG);
 //
 // Set id of filter B2_F3 to 3
 //
 CANSetFilter(CAN_FILTER_B2_F3,3,CAN_CONFIG_XTD_MSG);
 //
 // Set CAN module to NORMAL mode
 //
 CANSetOperationMode(CAN_MODE_NORMAL, 0xFF);
 //
 // Configure LCD
 //
 Lcd_Config(&PORTC,4,5,0,3,2,1,0); // LCD is connected to PORTC
 Lcd_Cmd(LCD_CLEAR);               // Clear LCD
 Lcd_Out(1,1,"CAN BUS");           // Display heading on LCD
 Delay_ms(1000);                   // Wait for 2 seconds
 //
 // Program loop. Read the temperature from Node:COLLECTOR and display
 // on the LCD continuously
 //
 for(;;)                  // Endless loop
 {
  Lcd_Cmd(LCD_CLEAR);     // Clear LCD
  Lcd_Out(1,1,"Temp = "); // Display "Temp = "
  //
  // Send a message to Node:COLLECTOR and ask for data
  //
  data[0] = 'T';                    // Data to be sent
  id = 500;                         // Identifier
  CANWrite(id, data, 1, send_flag); // send 'T'
  //
  // Get temperature from node:COLLECT
  //
  dt = 0;
  while(!dt) dt = CANRead(&id, data, &len, &read_flag);
  if (id == 3) {
   temperature = data[0];
   ByteToStr(temperature,txt); // Convert to string
   Lcd_Out(1,8,txt);           // Output to LCD
   Delay_ms(1000);             // Wait 1 second
  }
 }
}

Figure 9.17: DISPLAY program listing

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 = 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. Both mask 1 and mask 2 are set to all 1’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.

Filter 3 for buffer 2 is set to value 3 so that identifiers having values 3 are accepted by the receive buffer.

The operation mode is then set to NORMAL. The program then configures the LCD and displays the message “CAN BUS” for one second on the LCD.

The main program loop executes continuously and starts with a for statement. Inside this loop the LCD is cleared and text “TEMP =” is displayed on the LCD. Then character “T” is sent over the bus with the identifier equal to 500 (the COLLECTOR node filter is set to accept identifier 500). This is a request to the COLLECTOR node to send the temperature reading. The program then reads the temperature from the CAN bus, converts it to a string in array txt, and displays it on the LCD. This process repeats after a one-second delay.

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