Standard ULCAR Asynchronous Null Modem

function        pin                             pin
                 1 ----------------------------- 1
TXD              2 ----------------------------- 3
RXD              3 ----------------------------- 2
RTS              4 --+-------------------------- 8
CTS              5 --+
DSR              6 -----------------------------20
                 7 ----------------------------- 7
DCD              8 --------------------------+-- 4
                                             +-- 5
DTR             20 ----------------------------- 6