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Standard USB TTL cable and 4D USB TTL cable compatibility

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  • Standard USB TTL cable and 4D USB TTL cable compatibility


    I hooked up my oLED-160-G2 today. It's really nice. I'm trying to get the display to talk to VCP COM3 in Workshop 4, however things aren't quite as I'd hoped.

    Using a standard USB -> TTL cable (4-pin [gnd, tx, rx, and 5v] FT232R-based cable) makes the oLED come to life with the left-to-right scrolling information screen. It really does look nice! However, when I go to the Comms tab in Workshop 4 and hit the red circle underneath COM3, it times out with the message "Device is not responding" and the button stays red. (screenshot:

    I noticed that the 4D Systems cable ( uses 5 pins, the additional pin being used for Reset. I also noticed that pulling pin 9, Reset, low by shorting it against pin 7, gnd, caused the unit to reset as you'd expect.

    Intrigued, I played some timing games with Workshop 4 and sure enough it's possible to force it to detect the oLED-160 through a standard USB/TTL: simply short pin 7 & 9 on the oLED-160 (causing it to reset) and then immediately hit the red circle button in Workshop 4. I got the response "oLED160-G2 [2.5]" (screenshot:

    My guess is that the additional 5th line on the 4D systems USB/TTL cable is controlled by software and can be used to force a display device to reboot and handshake. This... feature... is not available on my 4-pin cable, but given that my computer can clearly use my standard USB/TTL cable to talk to the oLED, is there a quick hack I can use to program the oLED-160 without having to purchase one of 4D's $20 USB/TTL cables?

    Thank you,

  • #2
    If you have a cable that brings out DTR you can use You can convert it to reset using something like this

    The problem with the cheap cables is generally that they don't have DTR available.

    As you have found your hack can 'normally' be used. You can even use it to program the display.

    However, if you use the hack to load a PmmC there is a possibility of bricking your display, so beware.


    • #3
      Thanks for the response. I could go ahead and build the high pass / DC-blocking pass circuit you linked to, but I think I'll just go ahead and return my USB/TTL cable and buy the proper uUSB-PA5-II from SparkFun.