LPT problem

Discussion in 'The Projects Forum' started by natann999, Feb 27, 2013.

  1. natann999

    Thread Starter New Member

    Dec 11, 2012
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    hi
    in my project i use an altera kit that works at 3.3Volt.
    in my the project i send data from the computer directly to the altera (this part works) via the LPT port. the problem is that i need to send data back to the computer from the altera but the altera works at 3.3v and the computer works at 5v.
    what can i do?
    thank you for your attention
     
  2. tshuck

    Well-Known Member

    Oct 18, 2012
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    If you have the option of open-collector signalling, you can use pullup resistors to 5V. Otherwise, you can use a level shifter.

    This is a pretty good read...
     
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  3. natann999

    Thread Starter New Member

    Dec 11, 2012
    11
    0
    first i want to thank you for your help
    second i dont know if you understood that i am using one cable for the communication so any thing i do should work both ways. and if its relevant
    and third do you have an example for a bi-directional level shifter
    and last thing whats open-collector signalling???
    and again thank you very much
    AND sorry for all the and
     
  4. ScottWang

    Moderator

    Aug 23, 2012
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    Try ULN2803 and adding 8 pull up resistors.
     
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  5. tshuck

    Well-Known Member

    Oct 18, 2012
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    natann999 likes this.
  6. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    App Note on bi-directional level shifters

    If your bus is going to be input for one cycle, say, when strobe is enabled, and strobe is disabled for the incoming data, then a 74HC245 is easily used and low cost.

    If you don't have a way to sense/synchronize direction on a wire, such as an I²C bus, you'll need to read the app note linked above.
     
  7. t06afre

    AAC Fanatic!

    May 11, 2009
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    What altera chip are you using? Some Altera chips are able to handle 5 volt
     
  8. tshuck

    Well-Known Member

    Oct 18, 2012
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    It's probably a FPGA or CPLD with LVTTL I/O... If that's the case, the device cannot respond at the 5V level.
     
  9. t06afre

    AAC Fanatic!

    May 11, 2009
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    I know very well what Altera is. I asked because some of series can be made 5 volt tolerant with only a resistor. And other like the MAX 3000 may have 5 volt tolerant pins. I guess the OP uses the Byteblaster download cable ore a clone of it. As it is very simple. By the way here is low cost USB Altera programmer clone using a PIC micro. With some help of Google translate I was able to build one my self. And yes it works http://www.sa89a.net/mp.cgi/ele/ub.htm
     
  10. tshuck

    Well-Known Member

    Oct 18, 2012
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    I didn't explain what Altera is...:confused:
    The OP has already conveyed that the device is 5V tolerant(or at least the pins used are) in that the LPT can transmit to the Altera device properly. The problem is transmitting from the 3.3V device to the 5V device.
     
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