Chuck (I think) mentioned that he had never seen a proper specification of the RS232 (or whatever) signals. I think CCITT standard V.28 is much the same thing, and it can be found at : http://www.etsi.org/deliver/etsi_tbr/001_099/002/01_20_63/tbr_002e01c.pdf It certainly seems to have reasonable descriptions of the signal electrical characteristics. -tony