The Brahmi-derived writing systems have similar structure. So ISCII encodes letters with the same phonetic value at the same code point, overlaying the various scripts. For example, the ISCII codes 0xB3 0xDB represent . This will be rendered as കി in Malayalam, कि in Devanagari, as ਕਿ in Gurmukhi, and as கி in Tamil. The writing system can be selected in rich text by markup or in plain text by means of the ATR code described below. One motivation for the use of a single encoding is the idea that it will allow easy transliteration from one writing system to another. However, there are enough incompatibilities that this is not really a practical idea. See . ISCII is an 8-bit encoding. The lower 128 code points are plain ASCII, the upper 128 code points are ISCII-specific. In addition to the code points representing characters, ISCII makes use of a code point with mnemonic ATR that indicates that the following byte contains one of two kinds of information. One set of values changes the writing system until the next writing system indicator or end-of-line. Another set of values select display modes such as bold and italic. ISCII does not provide a means of indicating the default writing system.
Codepage layout
The following table shows the character set for Devanagari. The code sets for Assamese, Bengali, Gujarati, Gurmukhi, Kannada, Malayalam, Oriya, Tamil, and Telugu are similar, with each Devanagari form replaced by the equivalent form in each writing system. Each character is shown with its decimal code and its Unicode equivalent.
Special code points
; INV character—code point D9 : The INV character is used as a pseudo-consonant to display combining elements in isolation. For example, क + ् + INV = क्. The Unicode equivalent is. ; ATR character—code point EF : The ATR character followed by a byte code is used to switch to a different font attribute or language, up to the next ATR sequence or the end of the line. This has no direct Unicode equivalent, as font attributes are not part of Unicode, and each script has a distinct set of code points. ; EXT character—code point F0 : The EXT character followed by a byte code indicates a Vedic accent. This has no direct Unicode equivalent, as Vedic accents are assigned to distinct code points. ; Halant character ्—code point E8 : The halant character removes the implicit vowel from a consonant and is used between consonants to represent conjunct consonants. For example, क + ् + त = क्त. The sequence ् + ् displays a conjunct with an explicit halant, for example क + ् + ् + त = क्त. The sequence ् + ़ displays a conjunct with half consonants, if available, for example क + ् + ़ + त = क्त. ; Nukta character ़—code point E9 : The nukta character after another ISCII character is used for a number of rarer characters which don't exist in the main ISCII set. For example क + ़ = क़. These characters have precomposed forms in Unicode, as shown in the following table.
