https://devzone.nordicsemi.com/f/nordic-q-a/20371/ttl-and-rs232Hi, I want to know that what is the different between RS232 and TTL. I want to know that can we two RS232 to TTL converters back to back in the wire ??en-USTelligent Community 13Mon, 20 Mar 2017 09:28:41 GMThttps://devzone.nordicsemi.com/thread/79412?ContentTypeID=1Mon, 20 Mar 2017 09:28:41 GMT137ad170-7792-4731-bb38-c0d22fbe4515:7d35a927-3bc8-4be8-98c4-e8523d692ff7Sigurd<p>What converter are you using ?</p><div style="clear:both;"></div>https://devzone.nordicsemi.com/thread/79411?ContentTypeID=1Fri, 10 Mar 2017 13:10:37 GMT137ad170-7792-4731-bb38-c0d22fbe4515:29607832-3ef9-434e-b9d6-ad5af098776bUsman Rashid<p>Thanks for the answer.</p> <p>We have TTL to RS232 cable but when we add RS232 to TTL and then TTL to usb so we can not send the AT commands.</p> <p>Is it possible to use the converter back to back in such configurations ?</p><div style="clear:both;"></div>https://devzone.nordicsemi.com/thread/79410?ContentTypeID=1Fri, 10 Mar 2017 11:55:44 GMT137ad170-7792-4731-bb38-c0d22fbe4515:cd238004-ccab-4963-8e04-85f91a447cb9Sigurd<p>Hi,</p> <p>With the RS-232 standard a logic high (&#39;1&#39;) is represented by a negative voltage (from -3V to -25V), while a logic low (&#39;0&#39;) is a positive voltage (from 3V to 25V). With TTL (transistor-transistor logic), a logic low is 0V, and a logic high is usually the supply voltage (typical 3.0V on the nRF51). If you want use RS232 with the nRF5x, you need to add a RS232 transmitter/receiver, e.g. MAX232.</p><div style="clear:both;"></div>