Hello everyone,
I am working on a project and I need your help with a project I am working on.
I have MPLab on Mac using XC8. Also I am using PIC16F887
I want to control a DMX512 device. (for those who don't know what a DMX512 protocol is, check this link http://www.dmx512-online.com/packt.html)
I am trying to send information to my DMX512 controller, but I need to be send a byte (0-255). Is there a way to set up a pin to send it without using the TX pin (because it is already connected to a bluetooth module)
So I need the pin to transform the byte to bits and send 8 bits to the DMX controller.

I hope I was clear and thanks for your help in advance.
Regards

 

If you search for bit-bang serial you will find plenty of code around.

 

You just turn the pin On and Off to simulate 0 and 1 bits of the byte. Like Albert said, bit-bang.

 

yes but i have any number between 0 and 255 which means 00000000 and 11111111. I have 256 different combinations. definitely there is something that can translate the number I have to the corresponding bit-banging instead of writing a code for every number or combination.

 

yes but i have any number between 0 and 255 which means 00000000 and 11111111. I have 256 different combinations. definitely there is something that can translate the number I have to the corresponding bit-banging instead of writing a code for every number or combination.

It is called function library. If nobody before you have written one, then you be the first and blaze the trail for the generations to come.

 

Also, doing 256 cases is valid way to do it, but, like you said, a lot of work.
You should be able to do it smarter than that, you should be able to send 8 bit binary to the function, the function runs through the individual bits. If bit is 1, turn pin On. If bit 0, turn pin Off. I am thinking such a function would have maybe 15-20 lines of code.

 

There is this function that I found on wikipedia but to be honest I am not an expert in coding, I am still learning, so if anyone can explain to me what it means maybe I can build up from here:

// transmit byte serially, MSB first
void send_8bit_serial_data(unsigned char data)
{
   int i;

   // select device
   output_high(SD_CS);

   // send bits 7..0
   for (i = 0; i < 8; i++)
   {
       // consider leftmost bit
       // set line high if bit is 1, low if bit is 0
       if (data & 0x80)
           output_high(SD_DI);
       else
           output_low(SD_DI);

       // pulse clock to indicate that bit value should be read
       output_low(SD_CLK);
       output_high(SD_CLK);

       // shift byte left so next bit will be leftmost
       data <<= 1;
   }

   // deselect device
   output_low(SD_CS);
}

Can anyone explain this "if (data & 0x80)" This might solve my problem.

 

Can anyone explain this "if (data & 0x80)" This might solve my problem.

Masking I think.

 

yes but i have any number between 0 and 255 which means 00000000 and 11111111. I have 256 different combinations. definitely there is something that can translate the number I have to the corresponding bit-banging instead of writing a code for every number or combination.

Please: do look up what 'bit-banging' means

 

Can anyone explain this "if (data & 0x80)" This might solve my problem.

data & 0x80 does a bitwise 'and' function between the data value and 0x80 ( = binary '10000000'). So if bit 7 of data is set the result is 0x80, otherwise the result is zero. So it checks the most significant bit of data. Then later we have data <<= 1; which shifts the bits of data one place to the left, ready to check the next bit of data.

 

So just to see if I got it right. It checks bit 7, compares it with 0x80, if both are 1 (meaning the bit 7 in data is 1), then data<<=1, it moves wherever the value of bit 6 into bit 7 and then compares it. Is that right?

 

Yup
Edited to add:
I'll expand data & 0x80. Let's say data is 10101010
data 10101010
0x80 10000000 then 'and these tow together bit by bit
= 10000000 as this is not zero, 'C' counts it as true
data <<= 1 left shift data
data 01010100 '0' is shifted into bit 0
0x80 10000000 repeat the bit by bit 'and'
= 00000000 as this is zero, 'C' treats it as false
... and so on ...

 

How about this some inspiration from this app. note: AN1076 "Using a PIC Microcontroller for DMX512 Communication"

 

Kjeldgaard, this is really good. But I am working with C and I know only the very basics of assembly.
Albert, thank you for your help, this solved my question

 

one more question, for MPLAB XC8, do I need to let the clock advance one step?

 

one more question, for MPLAB XC8, do I need to let the clock advance one step?

These lines handle the clock transition:
// pulse clock to indicate that bit value should be read

• output_low(SD_CLK);

• output_high(SD_CLK);

 

would they work also on MPLAB?
I put it and it gave me an error after trying to build it.
if I just put this, won't it be enough?

            for (int i = 0; i < 8; i++){
                if (data & 0x80)
                PORTCbits.RC2=1;
                else
                PORTCbits.RC2=0;
                data <<= 1;
                }

The data<<=1; will let the clock forward while the port is set to HIGH or LOW

 

DMX runs at 250,000 baud.

Bit banging at that speed is not going to be so easy.

4 Microseconds per bit...

Swap the UART to the DMX and bit-bang the Bluetooth.

 

well that opens up a lot more questions for me.
Can you help me figure out the bit-bang sequence for the receiving?
I can store the bits in an array then combine to receive the byte (which I don't know how to make). You tell me if there is another way.
also how will I be able to get the timing right for this process?

 

Can you help me figure out the bit-bang sequence for the receiving?

If you are sending bytes as per a established protocol, your receiver should be suitable to interpret it.

Or are you trying to implement both ends?

/EDIT to add

You said in the OP that you have a controller.

I suggest you draw the sequence of bits yourself for a certain value as it should be produced by your pin and then imagine if you have to code it, no matter what ridiculous it could look.

The document that you recommended us to check, you should read again, I think.
EDIT/