I have used some I/O modules that use this "token-ring" rs-232 scheme. It works pretty well except that the more modules that you string together the longer the received data takes to get back to the computer. - -Mark >>> Robert Lunn 24 September 1996 7:14 pm >>> Hmm, token-ring RS-232... I'm not sure why you'd bother, given that the only practical difference on the remote nodes is a different transceiver chip.