Eight Ones

EO, or Eight Ones, is an 8-bit EBCDIC character code represented as all ones (binary 1111 1111, hexadecimal FF).

As a control code

Eight Ones, as an EBCDIC control code, is used for synchronisation purposes, such as a time and media filler.[1] In Advanced Function Presentation code page definition resource headers, setting at least the first two bytes of the field for the eight-byte code page resource name (which is encoded in code page 500) to Eight Ones (0xFF) constitutes a "null name", which is treated as unset.[2]

Mapping

When translated from the EBCDIC character set to code pages with a C1 control code set, Eight Ones is typically mapped to hexadecimal code 0x9F, in order to provide a unique character mapping in both directions.[3][4] Prior to 1986, however, the C1 control code 0x9F was usually mapped to EBCDIC 0xE1, which was frequently used as a numeric (figure) space in code pages at the time (including the pre-1986 version of code page 37).[5] The Unix dd utility follows the earlier convention, mapping the C1 code 0x9F to EBCDIC 0xE1, and mapping 0xFF (Eight Ones) to 0xFF.[6]

As a graphical character

While Eight Ones is treated as a control code by IBM EBCDIC infrastructure, EBCDIC code pages from Fujitsu Siemens used on the BS2000 system frequently use it for a graphical character, most often the tilde.[7] In these cases, the C1 control code 0x9F is mapped to a different location in the EBCDIC code page, most commonly 0x5F.[8]

See also

References
  1. IBM. "Appendix G-1. EBCDIC control character definitions". Character Data Representation Architecture. Archived from the original on 2018-09-11.
  2. AFP Consortium; IBM (2015). "BCP – D3A887 – Begin Code Page" (PDF). Font Object Content Architecture Reference (7th ed.). p. 126. AFPC-0007-06, S544-3285-06.
  3. Umamaheswaran, V.S. (1999-11-08). "3.3 Step 2: Byte Conversion". UTF-EBCDIC. Unicode Consortium. Unicode Technical Report #16.
  4. Steele, Shawn (1996-04-24). cp037_IBMUSCanada to Unicode table. Microsoft/Unicode Consortium.
  5. IBM (2018) [1990, 1995]. "Character Data Representation Architecture (CDRA)". p. 327. Prior to 1986, ISO-8 X'9F' (APC) mapped to EBCDIC X'E1'. This control code point is a graphic code point. It was previously used as numeric space character in many EBCDIC SBCS coded character sets, and with the latest revised CECPs, the numeric space character has been replaced with DIVISION SYMBOL.
  6. IEEE; The Open Group (2018). "dd - convert and copy a file". The Open Group Base Specifications Issue 7, 2018 edition. IEEE Std 1003.1-2017.
  7. "7.3 Supported line codes and BS2000 EBCDIC codes". XHCS V2.0—8-Bit Code and Unicode Processing in BS2000/OSD. Fujitsu Siemens Computers. 2007. pp. 147–194.
  8. "EBCDIC Character Set "OSD_EBCDIC_DF04_1"". IANA. 2004.
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