An ITU-T recommendation on electrical characteristics for unbalanced {double-CUrrent interchange cirCUits} operating at {data signalling rates} nominally up to 100 kbps. This recommendation is also included but not published in ITU-T X series under alias number X.26. The cirCUit defined in this standard is used in other serial line standards such as EIA-232 and EIA-423, that implement single ended communication. (2002-10-05)