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Question about the "Parallax USB to Serial (RS-232) Adapter". — Parallax Forums

Question about the "Parallax USB to Serial (RS-232) Adapter".

RonPRonP Posts: 384
edited 2011-12-04 13:56 in General Discussion
Hello All,

I have found myself needing to make up a ISP Serial Cable for another uController. My laptop dosn't have a Serial Port but I do have a "Parallax USB to Serial (RS-232) Adapter". I have read in these forums before that not all USB to Serial Adapters work with Parallax Products. Question is will Parallax's USB to Serial work just like a regular Serial Port? I don't know if it was made to support Parallax's products only or work like a regular serial port. There is no schematic or anything on the product page for me to try and figure it out, not that I would know how anyway. I don't want to make this ISP thing if it's not going to work, I can just order a programmer but I don't want to wait.

Thanks

Ron

Comments

  • Dr_AculaDr_Acula Posts: 5,484
    edited 2011-12-04 03:31
    Yes it will work like a regular serial port but I'd like to see a schematic. Are the RS232 lines 0V/5V or -9/+9V ?

    I'm actively working on this problem - my PC has a proper RS232 serial link but many computers don't and I've been curious for some time exactly why some $2 ebay USB to serial cables work and some don't. I'm getting closer to a solution and am awaiting a reply from Parallax support at the moment.

    If you want to test out your cable, first test is to plug it in and (in xp) start/control panel/system/hardware tab/ports and when you plug and unplug the adapter you should see it come up in the list. That also tells you which serial port it is.

    If you want to check for true RS232 voltages, plug it in and measure the volts between pin 5 (gnd) and pin 3 (data out) and you should get something like minus 9V. If you get zero volts, it may not work in all situations as 0V is usually interpreted as an inactive signal, but technically the RS232 standard does not allow volts between -3V and +3V.
  • RonPRonP Posts: 384
    edited 2011-12-04 10:55
    Thanks Dr. Acula,

    Here is a link to what I need to make ISP Programmer there is a schematic there. I did see the USB adapter show up in Device Manager. I'll check the voltage between pin 5 and 3.

    Ron
  • RonPRonP Posts: 384
    edited 2011-12-04 12:25
    Voltage between PIN5 (GND) and PIN3 (DATA OUT) = -9.80v . Going to the shack to get the 2 diodes that I don't have on hand, and see if it works.

    Ron
  • Dr_AculaDr_Acula Posts: 5,484
    edited 2011-12-04 13:56
    -9.8V is perfect - that means it is a standard RS232 device. Good news!
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