Details
NOTE: This table presumes the space called "1" by Baudot and Murray is rightmost, and least significant. The actual order of transmission varied by manufacturer.
In ITA2, characters are expressed using five bits. ITA2 uses two code sub-sets, the "letter shift" (LTRS), and the "figure shift" (FIGS). The FIGS character (11011) signals that the following code is to be interpreted as being in the FIGS set, until this is reset by the LTRS (11111) character. "ENQuiry" will trigger the other machine's answerback. It means "Who are you?"
CR is carriage return, LF is line feed, BEL is the bell character which rang a small bell (often used to alert operators to an incoming message), SP is space, and NUL is the null character (blank tape).
Note: the binary conversions of the codepoints are often shown in reverse order, depending on (presumably) from which side one views the paper tape. Note further that the "control" characters were chosen so that they were either symmetric or in useful pairs so that inserting a tape "upside down" did not result in problems for the equipment and the resulting printout could be deciphered. Thus FIGS (11011), LTRS (11111) and space (00100) are invariant, while CR (00010) and LF (01000), generally used as a pair, result in the same output when the tape is reversed. LTRS could also be used to overpunch characters to be deleted on a paper tape (much like DEL in 7-bit ASCII).
The sequence RYRYRY... is often used in test messages, and at the start of every transmission. Since R is 01010 and Y is 10101, the sequence exercises much of a teleprinter's mechanical components at maximum stress. Also, at one time, fine-tuning of the receiver was done using two coloured lights (one for each tone). 'RYRYRY...' produced 0101010101..., which made the lights glow with equal brightness when the tuning was correct. This tuning sequence is only useful when ITA2 is used with two-tone FSK modulation, such as is commonly seen in Radioteletype (RTTY) usage.
US implementations of Baudot code may differ in the addition of a few characters, such as #, & on the FIGS layer. The above table represents the US TTY code.
The Russian version of Baudot code (MTK-2) used three shift modes; the Cyrillic letter mode was activated by the character (00000). Because of the larger number of characters in the Cyrillic alphabet, the characters !, &, £, and BEL were omitted and replaced by Cyrillics.
Read more about this topic: Baudot Code
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