Baudot Code ITA2 Encoder and Decoder

What is Baudot Code (ITA2)?

The Baudot Code is a landmark in telecommunication history. Invented by French engineer Émile Baudot in the 1870s, it was the first character set to use a **5-bit digital code** to represent letters, numbers, and symbols. The system was later standardized internationally as **ITA2 (International Telegraph Alphabet No. 2)** and became the absolute standard for teleprinter, telex, and early computing systems.

How 5-Bit Modal Shifts Work

With exactly 5 bits, there are only 32 unique binary combinations ($2^5 = 32$). To represent the entire alphabet, numbers, and punctuation, the code uses a **modal shift state** system:

Letters Mode (LTRS): When in this mode, subsequent codes are interpreted as alphabet characters (A-Z).
Figures Mode (FIGS): When in this mode, subsequent codes are interpreted as numbers or punctuation marks.

To switch between these states, the sender transmits special shift character codes:

LTRS Shift (11111): Shifts the teleprinter or terminal into Letter mode.
FIGS Shift (11011): Shifts the teleprinter or terminal into Figure mode.

Once a shift code is received, the system stays in that mode until the opposite shift code is sent. This clever strategy allows 5 bits to represent up to 60 distinct characters!

Example: Encoding "HELLO 9"

Standard MSB representation:

H      E      L      L      O      [SPC]  [FIGS] 9
10100  00001  10010  10010  11000  00100  11011  11000

Note how the FIGS Shift (11011) is automatically injected before the number 9 to switch the mode.

Key Features of Our Baudot Code Tool

Bidirectional Translation: Easily encode standard plain text into 5-bit binary sequences, or decode raw binary streams back into text.
Interactive Stream Map: View a detailed step-by-step layout of each chunk showing automatically injected shifts.
Customizable Bit Order: Support standard **MSB-first** (Most Significant Bit) or standard teleprinter **LSB-first** (Least Significant Bit/Reversed) representation.
Configurable Spacing: Display output with spaced chunks, comma separators, or as a continuous binary stream.

Frequently Asked Questions

Why is LSB-first (Least Significant Bit) order used in teleprinters?

Historically, electromechanical teleprinters transmitted the least significant bit (LSB) first over transmission lines because it simplified the mechanical distributor mechanisms used to serialize and deserialize the pulses. Our tool supports both formats.

What characters are identical in both Letters (LTRS) and Figures (FIGS) modes?

Functional control codes like Space (00100), Carriage Return (01000), and Line Feed (00010) remain identical in both states to ensure printing layouts don't break during state changes.

What is the difference between Baudot and ASCII?

Baudot is a 5-bit code that relies on modal shifting to represent 60 characters. ASCII is a 7-bit code (or 8-bit extended ASCII) which has 128 unique positions, eliminating the need for state-based shift characters and reducing decoding state complexity.