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Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
im getting nothing, and ive followed the directions and advice from a tutorial not associated with parallax that has high positive feedback.
i get a pic like this :
my cord looks like this:
Laptop -> USB - serial cable -> serial connector -> embedded device PCB.
from the serial to embedded device looks like this:
LAptop: *************************** Device: Pin2 Comp Recieve ......= blue wire ------- TXO <- Note it could be a D or an O, I cant tell. Pin3 Comp Transmit ....= White wire ------ RXI <- Note its not labled RXD Pin4 Comp Ready ........= Yellow wire ----- DTR Pin5 Ground ...............= Black (GND) ---- GND
* i wonder if pins 2 and 3 are reversed ? should i also attach the ground to the shield ? both should be close to zero volts, or will that let noise in ?
Someone check the cable to make sure i didnt botch it:
Registered Member #3215
Joined: Sun Sept 19 2010, 08:42PM
Location:
Posts: 780
check if your USB to serial converter is 3.3V or 5V signal level
every basic USB to serial convertre is 3.3V nowadays, which is not suitable for microcontroller use if it is not specifically a 3.3V serial enabled device
you either have to make a level shifter or use a 5V serial converter
Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
Shrad wrote ...
check if your USB to serial converter is 3.3V or 5V signal level
every basic USB to serial convertre is 3.3V nowadays, which is not suitable for microcontroller use if it is not specifically a 3.3V serial enabled device
you either have to make a level shifter or use a 5V serial converter
my serial converter puts out -8, 0 and 8 volts apparently, my parallax device is 3.3 and 5 volt capable on its serial pins.
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
Ah, there's your problem, you are feeding RS232 levels into a TTL port on a microcontroller. IIRC, the RS232 level shifter chip also inverts the polarity of the signal, so it won't work. You need to either hack into the USB-to-serial dongle and bypass the level shifter, or shift the levels back to TTL using a MAX232 or similar chip.
Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
Steve Conner wrote ...
Ah, there's your problem, you are feeding RS232 levels into a TTL port on a microcontroller. IIRC, the RS232 level shifter chip also inverts the polarity of the signal, so it won't work. You need to either hack into the USB-to-serial dongle and bypass the level shifter, or shift the levels back to TTL using a MAX232 or similar chip.
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How do i use Parallax Serial Terminal ?
