re how is a null modem cable kevin kimmell computer science german undergrad ke kimmell vax cns muskingum edu wrote i am interrested in the extrodinarily simple concept of the null modem cable actually i have no idea so don t count that last statement what i m asking is what pins does it use or what are it s specifications i just want to solder one myself instead of buying one i don t even know what port is used db db pin pin name eia ccitt dte dce description fg aa frame ground td ba transmitted data rd bb received data rts ca request to send cts cb clear to send dsr cc data set ready sg ab signal ground dcd cf data carrier detect positive dc test voltage negative dc test voltage qm equalizer mode sdcd scf secondary data carrier detect scts scb secondary clear to send std sba secondary transmitted data tc db transmitter clock srd sbb secondary receiver clock rc dd receiver clock dcr divided clock receiver srts sca secondary request to send dtr cd data terminal ready sq cg signal quality ri ce ring indicator ch data rate selector ci data rate selector tc da transmitted clock from another posting in c s i p h sorry don t know the author connecting devices normally a wire connection is used connect gnd to gnd rxd to txd txd to rxd dtr to dsr dsr to dtr rts to cts cts to rts if a modem is connected add lines for the following ri dcd if software wants it connect dcd to cts and dcd to cts beware while pcs use pin for rxd and pin for txd modems normally have those pins reversed this allows to easily connect pin to pin pin to pin etc if you connect two pcs cross rxd and txd if hardware handshaking is not needed a so called null modem connection can be used connect gnd to gnd rxd to txd txd to rxd additionally connect if software needs it rts to cts dcd rts to cts dcd dtr to dsr dtr to dsr you won t need long wires for these the null modem connection is used to establish an xon xoff transmission between two pcs see software section for details remember the names dtr dsr cts rts refer to the lines as seen from the pc this means that for your data set dtr rts are incoming signals and dsr cts are outputs end michael michael jester gun de michael gerhards preussenstrasse germany neuss voice
