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# 2025-06-21 - ITA-2 Telegraph Code |
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Western Union Bicycle Messengers (1911) (Smithsonian) |
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A friend sent me a link to a video of someone creating art on an |
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old-school mechanical typewriter. Following up, i found typewriter |
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art books on the Internet Archive, one of which is dated 1936. |
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How To Make "Typeys" (1936) |
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Art Typing |
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I sent these links to another friend. I called it an example of |
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ASCII art from 1936. This friend informed me that ASCII didn't |
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exist in 1936. |
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Doing a little research, i found that what existed in 1932 was |
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ITA-2 telegraph code, which is encoded as 5-bit values that can be |
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punched on 5-hole paper tape. A perfect rabbithole to go down on |
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this rainy day. :-) |
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ITA-2 alphabet on 5-hole tape |
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I wrote a small AWK script to convert between ASCII and ITA-2. |
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The first limitation i noticed was that ITA-2 cannot represent every |
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ASCII character. Like my keyboard, ITA-2 lacks lowercase letters. |
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I wrote a small extension to work around this: any ASCII character |
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that doesn't exist in ITA-2 would get encoded as a five character |
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escape sequence. |
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* FIGURES |
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* ALLSPACE_NOTINUSE |
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* Octal digit1 |
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* Octal digit2 |
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* Octal digit3 |
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Why octal? Just for the fun of it. |
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Below is ita2.awk which converts between ASCII and ITA-2. |
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ita2.awk |
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Next i wrote an even smaller script to convert between ITA-2 and |
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simulated paper tape. Slackware's bsd-games package includes a `ppt` |
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command that simulates 8-hole tape. Below is ppt5.awk, which |
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simulates 5-hole tape. |
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ppt5.awk |
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To get a "tape" version of the natural musical tones: |
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$ printf ABCDEFG | mawk -f ita2.awk | mawk -f ppt5.awk >tones.txt |
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$ pr -n -t tones.txt |
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1 ________ |
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2 | .oo| |
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3 |oo . o| |
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4 | oo.o | |
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5 | o . o| |
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6 | . o| |
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7 | oo. o| |
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8 |oo .o | |
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9 -------- |
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For the round trip: |
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$ mawk -f ppt5.awk decode tones.txt | mawk -f ita2.awk decode |
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ABCDEFG |
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In xterm i can see a cat emoji using the following command. |
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$ printf "\360\237\220\261" >cat.txt |
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$ cat cat.txt |
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🐱 |
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To get a "tape" encoding of that cat: |
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$ mawk -f ita2.awk cat.txt | mawk -f ppt5.awk >tape.txt |
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$ pr -2n -t tape.txt |
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1 ________ 12 |oo .oo| |
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2 |oo .oo| 13 | . | |
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3 | . | 14 |o .oo| |
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4 | . o| 15 |o .oo| |
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5 |o o. o| 16 |o o.o | |
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6 |o o.o | 17 |oo .oo| |
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7 |oo .oo| 18 | . | |
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8 | . | 19 |o .oo| |
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9 |o .oo| 20 |o o. o| |
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10 | . o| 21 |o o.oo| |
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11 | o.oo| 22 -------- |
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To send that cat on a round trip: |
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$ mawk -f ppt5.awk decode tape.txt | mawk -f ita2.awk decode |
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🐱 |
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To be silly, here's the paper tape with corresponding pohl code: |
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1 ________ 12 |oo .oo| oddy-pod |
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2 |oo .oo| oddy-pod 13 | . | pohl |
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3 | . | pohl 14 |o .oo| ahtah-pod |
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4 | . o| poot 15 |o .oo| ahtah-pod |
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5 |o o. o| ahtah-tot 16 |o o.o | ahtah-dye |
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6 |o o.o | ahtah-dye 17 |oo .oo| oddy-pod |
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7 |oo .oo| oddy-pod 18 | . | pohl |
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8 | . | pohl 19 |o .oo| ahtah-pod |
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9 |o .oo| ahtah-pod 20 |o o. o| ahtah-tot |
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10 | . o| poot 21 |o o.oo| ahtah-tee |
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11 | o.oo| tee 22 -------- |
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Pohl Code |
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For a sanity check, i found an photo of 5-hole tape for CSIRAC, the |
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first digital computer in Australia. |
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5-hole tape photo |
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CSIRAC |
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I manually keyed in the first 10 characters visible in the photo. |
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$ pr -n -t 5hole.txt |
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1 ________ |
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2 |ooo. o| |
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3 |ooo.o | |
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4 | .oo| |
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5 |o o.oo| |
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6 | o . | |
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7 | o. | |
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8 | o .oo| |
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9 | .oo| |
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10 |ooo. | |
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11 | o . | |
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12 -------- |
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Now to decode the virtual paper tape. |
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$ mawk -f ppt5.awk decode 5hole.txt |\ |
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mawk -f ita2.awk decode |\ |
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hexdump -C |
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00000000 58 56 41 51 0d 20 4a 41 4d 0d |XVAQ. JAM.| |
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0000000a |
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I guess this means it's working? Apparently the lines of text end |
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with CR only and no LF. |
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See also: |
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Computerphile Paper Tape Video |
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DIY Paper Tape Puncher |
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p.s. |
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To run these examples with mawk on DOS, you may need to set an |
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environment variable MAWKBINMODE=1 |
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To run these examples with gawk, you may need to set an |
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environment variable LC_ALL=C |
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tags: history,retrocomputing,technical |
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# Tags |
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history |
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retrocomputing |
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technical |
