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I'm trying to connect a device to my laptop using a TTL to USB converter like this one USB to TTL

but it doesn't works

so I tried the following configuration

(USB to Serial, RS232 to TTL and then to the device)

enter image description here

And works perfect.

Both (USB to Serial and USB to TTL) are using the PL2303 driver.

The question is why the USB to TTL didn't work? it uses a different protocol?

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  • \$\begingroup\$ I actually had issues with that prolific device also. It seemed to work in some PCs and not others. I just swapped to a different one. Never had an issue with an FTDI converter so if you want to be safe just stick with those types. \$\endgroup\$ – Cameron Aug 11 '16 at 5:00
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You may well have gotten bit by a fake Prolific 2303 chip.

The Prolific driver download site has a warning and also says how to detect the fakes.

Basically, check the Windows Device Manager. If your Serial/USB device shows a yellow warning triangle and has error code 10, then you have a fake. It will not work with newer Prolific drivers.

You might find an old Prolific driver that will work with your device. There are lots of sites on the internet discussing this, and lots of advice on finding old drivers.

You might also just save yourself the time rooting around the internet and buy or order an adapter from someplace reliable so that you don't get burned by another fake and don't have to worry about the drivers.

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These USB-TTL converters with PL2303 chips are crap. I've got many problems with these sticks, i.e. one described here. The problem lies in PL2303 chip - 99,9% of these terribly cheap sticks have counterfeited ICs. They may look like original ones from Prolific, but obviously they do not. Differences are very subtle, for example mine have invalid production code.

As Artūras Jonkus said You should use stick with original chip, these from FTDI are great (but not cheap), and there is a small chance for buying counterfeited FTDI chips. Original Prolific chips are also very good, but there are plenty fake ones on the market. Also good USB-TTL chips without many fakes are from Cypress.

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  • \$\begingroup\$ My rule of thumb: if you paid less than $5 for a PL2303, CH340 or FT232RL, then you've got a fake. It will not work. \$\endgroup\$ – rustyx Mar 19 at 22:07
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There may be several problems. For begining, connect your TTL to USB converter to computer and measure if there are voltages that are supposed to be there (3.3V and 5V). Some converters might need additional jumpers to enable voltage rails on output. If everything is fine, proceed, if not - it's likely that something in pcb is broken. I don't think that's the case this time. You might try switching TX and RX wires because that's usual mistake and making sure that you've chosen right communication configuration (baud rate, stop, parity bits). If you have oscilloscope, I highly recommend to send something from your computer and see if it's transmitted; send something from device and make sure it's received.

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    \$\begingroup\$ I tried all, I don't have an oscilloscope but I did a loopback and works fine. I actually have 2 usb to ttl converters and same with both. \$\endgroup\$ – Gerardo Aug 11 '16 at 5:28
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    \$\begingroup\$ Switch RX and TX between themselves. Report results \$\endgroup\$ – Artūras Jonkus Aug 11 '16 at 6:37
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Connect conterter TX to its RX and type something in the terminal, you should see you characters, if you don't than the converter is definitely broken.

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  • \$\begingroup\$ He already did loopback test succesfully \$\endgroup\$ – Artūras Jonkus Aug 11 '16 at 12:03
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You just need to download older drivers for Usb to TTL prolific and it works. Had the same issue, i just downgraded from 3.8 to 3.0 drivers. Check the device manager on your windows under Ports if you see a yellow warning icon next to your device it is because of drivers. (This works for cloned PL2303, original works with new drivers)

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    \$\begingroup\$ This is a duplicate of the answer I posted 3 years ago. \$\endgroup\$ – JRE Jul 18 at 15:24

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