asking about the meaning of a dummy output

[boukamoha]

hi every one ..i have this part of the program ..

char dummy;
CE = 1;
Send_To_TC72(0x80);
dummy = SSPBUF;
Send_To_TC72(0x11);
CE = 0;
dummy = SSPBUF;
Delay200ms( );

can some one tell me exactlly the meaning of the dummy variable? and when can i use it...
thx in advance

 

[matthai]

hi
we need all program to understand dummy,
i think this is only a char named dummy.

 

[horace1]

hi every one ..i have this part of the program ..

char dummy;
CE = 1;
Send_To_TC72(0x80);
dummy = SSPBUF;
Send_To_TC72(0x11);
CE = 0;
dummy = SSPBUF;
Delay200ms( );

can some one tell me exactlly the meaning of the dummy variable? and when can i use it...
thx in advance

it looks as though the code is writing the value 0x11 into the control register (0x80) of a TC72 digital temperature sensor
the statements

dummy = SSPBUF;

reads the value in the SPI serial transmit/receive register (and then appears to discard it) before the next write. I don't think you need to do this but we have to see the rest of the code.
I tend to write the SPI buffer, wait for it to complete and then read it in a function so (this is for a PIC24)

// send one byte of data and receive one back at the same time
unsigned char writeSPI1( unsigned char i )
{
    SPI1BUF = i;                      	// write to buffer for TX
    while(!SPI1STATbits.SPIRBF) Nop();  // wait for transfer to complete
    return SPI1BUF;                    	// read the received value
}

 

[boukamoha]

hi horace1
thx for your response..in reality i want to connect two pic microcontollers using the spi protocol can you give me more details about this kind of connection with an example c code...
thx in advance

 

[horace1]

hi horace1
thx for your response..in reality i want to connect two pic microcontollers using the spi protocol can you give me more details about this kind of connection with an example c code...
thx in advance

should be no problem so long as the SPI configuration is the same in terms of baud rate and other parameters.
make one the master the other a slave? have a look at Microchip's sample code
**broken link removed**

 

[boukamoha]

ok i've got the aimed code ..thank you for help..
cheers..

 

[boukamoha]

hi horace1
i've read the codes from microship but i still didn't understand how to write to a microcontroller and get the response...for example in my case i want to perform a simple mathematical operation and send the comands from the first microcontroller to perform that operation in the second one , but the results will be displayed in LCD connected to the first microcontroller , so the question is how i can proceed to send the write and read commands , like we use to do in the TC72 digital sensor .
another question can you tell me please which registers in the SLAVE microcontroller should i work?
cheers..

 

[horace1]

have a look at
ww1.microchip.com/downloads/en/devicedoc/spi.pdf

it discusses SPI and the programming of a SPI master and slave with example code

 

[boukamoha]

thx.. now i'm doing a progress