MikroElektronika PIC Microcontrollers PIC18 Instrukcja Użytkownika Pobierz pdf (Strona 32)

The DISPLAY Processor

Like the COLLECTOR processor, the DISPLAY processor consists of a PIC18F258

microcontroller with a built-in CAN module and an MCP2551 transceiver chip. The

microcontroller is operated from an 8MHz crystal. The MCLR input is connected to

an external reset button. The CAN outputs (RB2/CANTX and RB3/CANRX) of the

microcontroller are connected to the TXD and RXD inputs of the MCP2551. Pins

CANH and CANL of the transceiver chip are connected to the CAN bus. An

HD44780-type LCD is connected to PORTC of the microcontroller to display the

temperature values.

The COLLECTOR Processor

The COLLECTOR processor consists of a PIC18F258 microcontroller with a

built-in CAN module and an MCP2551 transceiver chip. The microcontroller is

operated from an 8MHz crystal. The MCLR input is connected to an external reset

button. Analog input AN0 of the microcontroller is connected to a LM35DZ-type

semiconductor temperature sensor. The sensor can measure temperature in the range

of 0



C to 100



C and generates an analog voltage directly proportional to the

measured temperature (i.e., the output is 10mV/



C). For example, at 20



C the

output voltage is 200mV.

The CAN outputs (RB2/CANTX and RB3/CANRX) of the microcontroller are

connected to the TXD and RXD inputs of an MCP2551-type CAN transceiver

chip. The CANH and CANL outputs of this chip are connected directly to a twisted

cable terminating at the CAN bus. The MCP2551 is an 8-pin chip that supports

data rates up to 1Mb/s. The chip can drive up to 112 nodes. An external resistor

connected to pin 8 of the chip controls the rise and fall times of CANH and

CANL so that EMI can be reduced. For high-speed operation this pin should be

connected to ground. A reference voltage equal to VDD/2 is output from pin 5 of

the chip.

The program listing is in two parts: the DISPLAY program and the COLLECTOR

program. The operation of the system is as follows:



The DISPLAY processor requests the current temperature from the

COLLECTOR processor over the CAN bus

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MikroElektronika PIC Microcontrollers PIC18 Instrukcja Użytkownika Strona 32