Technical information

Serial Solutions What To Do First
RS232 signal lines.
TXD, Transmitted data an output from PC Data line.
RXD, Received data an input to PC Data line.
RTS, Request To Send an output from PC
CTS, Clear To Send an input to PC Handshake line.
DSR, Data Set Ready an input to PC
DCD, Data Carrier Detect an input to PC
DTR, Data Terminal Ready an output from PC Handshake line.
RI, Ring Indicator an input to PC. Used by Modems.
In some RS232 systems the handshake lines are not used or are
simply ignored. Only the transmitted data line, received data line
and the ground pins need be connected. This method, often
called ’the 3 wire handshake’, works well only if small amounts
of data are sent or if both devices are fast enough to deal with
any amount of data received. The ’3 wire handshake’ assumes
that all the traffic lights are always green and that data can be
sent at any time.
Every example in this chapter so far has used the ’3 wire
handshake’, so that the PC always believes it can send data. This
was specified just to get the data transfer going. The ’3 wire
handshake’ was specified in the NEWCOM.SYS driver by the
/Hr,4 parameter. Where r specifies the COM ports, r may be a
single port or a range of ports. For example:-
/H1,4 sets up no handshaking for COM1.
/H12,4 sets up no handshaking for COM12.
/H7-16,4 sets up no handshaking for COM7 to COM16.
Page 12 Chapter 1