Eight Ones
EO, or Eight Ones, is an 8-bit EBCDIC character code represented as all ones.Eight Ones, as an EBCDIC#Definitions of non-ASCII [EBCDIC controls|EBCDIC control code], is used for synchronisation purposes, such as a time and media filler. 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 to Eight Ones constitutes a "null name", which is treated as unset.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. 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. The Unix utility follows the earlier convention, mapping the C1 code 0x9F to EBCDIC 0xE1, and mapping 0xFF to 0xFF.While Eight Ones is treated as a control code by IBM EBCDIC infrastructure, EBCDIC code pages from Fujitsu [Siemens Computers|Fujitsu Siemens] used on the BS2000 system frequently use it for a graphical character, most often the tilde. In these cases, the C1 control code 0x9F is mapped to a different location in the EBCDIC code page, most commonly 0x5F.