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TTL to CMOS protection / recommendation

Former Member

Hi there,

 

I am creating an interface board for CNC equipment, the board will accept legacy parallel/TTL level inputs, however due to the need to support various devices I'll be using a CPLD or FPGA chip to allow custom configuration of each groups of boards.

 

I'm a little stuck as the 25 pin parallel port supports 17 signal pins and 1 ground pin, so looking for a recommendation for a low cost non-inverting buffer that can support that number of signal pins. The soul purpose of the buffer is to protect the 3.3v CMOS circuit from the potentially higher TTL voltages.

 

Xilinx recommend the MC74VHC1GT50 which is a small device, so looking for something of similar spec that can support the 17 signal pins. Would anyone have a recommendation for a device?

 

Many thanks

Paul

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  • 0

    Why not use a Cypress Semiconductor Psoc 4?

     

    It allows you to use TTL, CMOS and a variety of interface levels under firmware control.

     

    Saves you a lot of circuitry and detailed wiring.

     

    DAB

  • 0 in reply to DAB

    DAB, The reason I did not look at the PSoC is due to one seriously important factor ... my own stupidity. In fact I have used PSoC 4's in several projects and thus pulled out the documentation stored on my laptop, which is for the 4000 series, which only has 20 GPIO's and max of 28 pins. I had assumed the '4000' series spec sheet meant it covered 4100 and 4200. To say I was disappointed is an understatement as to my mind the PSoC 4 is perfect for this application, so perfect and so cheap I was even considering using 2 PSoC4's.

     

    Thanks to your suggestion I went back to the Cypress website and now see the 4100 and 4200 are entirely different series with their own spec sheets and that both support 55 GPIO's.

     

    Thank you so much!

     

    Paul

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  • 0 in reply to DAB

    DAB, The reason I did not look at the PSoC is due to one seriously important factor ... my own stupidity. In fact I have used PSoC 4's in several projects and thus pulled out the documentation stored on my laptop, which is for the 4000 series, which only has 20 GPIO's and max of 28 pins. I had assumed the '4000' series spec sheet meant it covered 4100 and 4200. To say I was disappointed is an understatement as to my mind the PSoC 4 is perfect for this application, so perfect and so cheap I was even considering using 2 PSoC4's.

     

    Thanks to your suggestion I went back to the Cypress website and now see the 4100 and 4200 are entirely different series with their own spec sheets and that both support 55 GPIO's.

     

    Thank you so much!

     

    Paul

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