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DMX lightcontrol using FPGA and RS-232 to DMX converter (part 1)

January 24th, 2011 1 comment

My last big project before I can start with my graduation internship is a DMX light controller using an FPGA and a RS-232 to DMX converter. I’m using the Altera DE2 development and education board containing a CycloneII FPGA. Combined with a DMX4ALL DMX player XS and a set of 4 RGB LED PAR’s this should become a nice system to demonstrate RS-232 communication on the DE2 board.

The core of the system will be a NIOS II processor. This gives me the opportunity to write C or C++ code for my program logic. Setting up the basics like the core NIOS II and a simple test program should be very simple according to several online university tutorials. Unfortunately, it took me longer than I expected. The standard pin assignment file for the DE2 board differs in naming for some DRAM pins compared with the naming used by the SOPC builder. There was also a bug in the Eclipse based software developer tool. After a lot of browsing through manuals and forums, some debugging and testing I finally managed to get the core system up and running.

I have uploaded an edited pin assignment file containing the DRAM pin modifications for the DE2 board and NIOSII. You can download this CSV file here. Two very clear and helpful tutorials can be found on the McMaster University website. The tutorials I have used are nios2-1 (mirror) and nios2-2 (mirror).

Now I could start with the fun part. Programming a simple test to send data over the RS-232 port. I managed to communicate with a laptop. But the DMX converter wouldn’t respond to the commands I sent. What could that be. Putty received the commands perfectly. Doh, of course. Most serial communication systems involve a TX and a RX signal. So does RS-232. What I need is a cross cable. I still don’t know why the communication with the laptop worked without a cross cable. The laptop probably has some sort of switching mechanism, like most of the ethernet connectors currently have. Transmitting data over RS-232 is very easy. It involves just a small piece of C code:

void UART1_T(unsigned char ch){
  while((IORD_ALTERA_AVALON_UART_STATUS(RS232_BASE) & 0x040) != 0x040){ ;}
  IOWR_ALTERA_AVALON_UART_TXDATA(RS232_BASE,ch);
}

Anyway, using a cross cable the converter finally responded to my commands. I wrote a small test program which changes the color of one RGB light. See the video below. When I continue on this project I will add links to the used manuals and add the code I used for my tests. That’s done.

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