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Have this small interface FTDI FT232RL to connect a Serial device to the computer via USB.

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It has been working well for most of my Serial applications, except today when I tried to use it for a Roboteq controller. While all settings are correct, characters are garbage.

The support tells me the FTDI device use TTL levels (0~3.3/5V) instead of RS232 (-9~+9V). Which seems to be unfortunately correct according to the FTDI doc.

Question

Is there a simple way to have this FTDI device consider RS232 levels, not TTL? (eg like shorting a couple of pins) The Roboteq device doesn't seem to be configurable in this regard.

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    \$\begingroup\$ No. You need a RS232 level converter circuit. \$\endgroup\$ – brhans Jan 7 '16 at 16:09
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    \$\begingroup\$ Typically you'd use TTL levels for short distances, usually on the same PCB or at least in the same enclosure. RS232 levels are better for longer distances (and other reasons too). \$\endgroup\$ – brhans Jan 7 '16 at 16:13
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    \$\begingroup\$ Watch out. Connecting full-swing RS232 to your FTDI device will likely damage the latter. Many "RS232" device actually use a limited voltage swing which is less likely to damage. But even in those cases, the TTL signal is inverted from the RS232 signal so you really need a converter. \$\endgroup\$ – DoxyLover Jan 7 '16 at 22:17
  • \$\begingroup\$ @DoxyLover thanks. too bad the ftdi doesn't handle rs232 in the first place... \$\endgroup\$ – e2-e4 Jan 8 '16 at 8:09
  • \$\begingroup\$ Why don't you buy usb-rs232 in your nearer shop? \$\endgroup\$ – Marko Buršič Jan 8 '16 at 11:40
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If you want to talk over USB it would be far faster and easier to just buy one of the many USB->RS232 converter cables than to mess around making that into one. I've seen them for as low as $7 USD online.

There are even cables with the FTDI chips in them so if you've been using the D2XX library you can continue doing so.

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Simple answer: No! You need a level converter, something like a Maxim MAX232 IC to convert from TTL (0-5V) to RS232 (+/-12V ish) signals

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