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Altera_Forum's avatar
Altera_Forum
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15 years ago

How to connect PC Rs232 to CIII FPGA Pins?

I have cyclone III Starter board, with its HSMC connector occupied with a daughter card. I had my design done but I couldn't find a way to send data at run-time to the board from My PC.

I am talking about end-user of my future board, not a development or testing phase issue. How can I make the end-user connect to my board and send data to it?

The data is very simple bytes, small and few. I need to connect the RS232 from my PC to the board FPGA Pins so I can implement a FIFO or so inside the FPGA with VHDL. This way I can write simple app on Windows to send data to the board.

If you know better solution than this, or know HOW to connect the JTAG 10 pins to become an RS232 interface please let me know.

The JTAG 10 pins are the only pins left on the board.

Can I convert them into an RS232 interface?

I have a tiny external board that converts the RS232 to TTL signals, four pins out. Can I connect this 4 pins to the JTAG 10 pins? How to do so?

Am I making sense? Please forgive my ignorant I am a beginner in this field.

Can You please help me with details on how "physically" can I do this?

Do you have better solution?

Please note that I wasted few months (really) trying to find a solution, including frustration with Nios Core. So Nios is not an option.

Also I can not pay 5000$ dollars for a USB core. Even if I can, how to connect any USB device to the board, as no pins left free else the JTAG 10 pins.

I appreciate your patient reading this, and I appreciate your input.

Thanks.

:confused:

3 Replies

  • Altera_Forum's avatar
    Altera_Forum
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    15 years ago

    The JTAG pins can't be used as regular I/O so you can't connect a RS232 converter to them and use it to communicate with thu PC. I think your only option is to do it through a USB blaster and the JTAG interface, using as an example the JTAG virtual interface component.

  • Altera_Forum's avatar
    Altera_Forum
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    15 years ago

    JTAG uses 4 signal (the other pins being Vcc,GND or NC) which are dedicated pins on the fpga. AFAIK you cannot use them as general purpose pins in your design.

    Surely jtag can emulate a serial port, which is what the Quartus debugger does: but in this case I think you need a specific hardware (USB blaster or similar) and a pc side driver/software in addition to the jtag serial port module in the fpga; your external converter board is far from being enough.

    For a RS232 interface (say UART, since rs232 are actually the phy signal levels) you simply need a single input and a single output signal, provided you don't require flow control, which would add one more input and one more output.

    If you can wire these two pins out of your board, this is quite easy to implement.

    Regards

    Cris
  • Altera_Forum's avatar
    Altera_Forum
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    15 years ago

    Thanks for the response.

    I thought about this solution: buying one of those breakout FPGA boards, and wire everything my self, this way I will find access to the FPGA pins to add a UART physical connector, or even USB-UART chip and connector.

    Does that sound reasonable?

    Well, I am not expert in wiring it, I know it is going to be much work, but possible, instead of 'not possible' on the starter board.

    My desgin doesn't take more than 1000 to 1500 LEs, so I though about a cheaper solution going down to CPLD but the number of IOs are not enough, I need 50 pins at least to replace the DVI HSMC board I have, and adding to the needed UART pins.

    Any idea of the best breakout board, that is easy to deal with?

    Thanks for your help.