RxD means Receive Data.

TxD means Transmit Data.

Where the "x" come from?

  • 7
    \$\begingroup\$ Rx is short for receive because I guess someone decided it was easier than writing "receive" all the time. Likewise for Tx/transmit. It's not specific to electronics, you see e.g. pilots saying "pax" for "passengers". \$\endgroup\$
    – user253751
    Jan 30 '16 at 13:01
  • 6
    \$\begingroup\$ This sort of word etymology question would probably be better on English.SE, in fact there's a related question that probably at least partially answers it: english.stackexchange.com/questions/229929/… \$\endgroup\$
    – PeterJ
    Jan 30 '16 at 13:05
  • 3
    \$\begingroup\$ I suspect the word "exchange" has something to do with it. See also PABX and MUX. But X could also mean "cross". \$\endgroup\$
    – Andy aka
    Jan 30 '16 at 13:14
  • 1
    \$\begingroup\$ @PeterJ That's an unusually sparse answer for ESE. The use of x as an abbreviation is much older than the technological examples given. Consider Rx (for prescription, which is short for Latin recipe). This is different from the X in Xmas, where X is the first letter of the Greek spelling of Christ (Χριστός). \$\endgroup\$ Jan 30 '16 at 14:40
  • \$\begingroup\$ english.stackexchange.com/questions/37394/… \$\endgroup\$
    – Andy aka
    Jan 31 '16 at 11:33

Comes from the 'good old days' of radio when Morse code ruled. Abbreviations abounded (c.f. text messages!), and TX was transmitter or transmit; RX was receiver or receive \$\cdot\cdot\cdot-\cdot-\$

  • 2
    \$\begingroup\$ "TT" or "RR" would be shorter in Morse code than "TX" or "RX". So why "X"? You might be right, but as a statement, this does not seem very compelling. One can argue whether etymology questions are suited for EE.SE, of course, but either way this is not an answer to such a question. \$\endgroup\$ Jan 30 '16 at 16:07
  • 3
    \$\begingroup\$ T and R would be even shorter. I just gave the history, I did not seek to explain why. But I suspect a lot has to do with the ease of keying and rhythmic sound of the keyed CW, e.g. TNX sounds much better the TKS for 'thanks'; PSE sounds better and is easier to key than PLS, for 'please', etc. You must remember that Morse code (or 'CW') is aural, not visual. \$\endgroup\$
    – Chu
    Jan 30 '16 at 16:29
  • \$\begingroup\$ Try "beef essence" in Morse :-) \$\endgroup\$
    – Russell McMahon
    Jun 23 at 9:32

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