Technical information

What To Do First Serial Solutions
A common RS232 handshake is the DTR /CTS handshake.
Here the traffic light signal is passed out of the PC to the
external device on its DTR wire. The traffic light signal from
the external device is brought in on the PC’s CTS wire.
The PC will only transmit, ie send, data when the CTS
input is green, ie logically true. The PC will stop transmitting
data when the CTS input is red, ie logically false.
When the PC is able to receive data it will set the DTR
output green, ie logically true. When it cannot accept any data it
will set the DTR output red, ie logically false.
The RS232 DTR/CTS handshake is was passed to the
NEWCOM.SYS driver by the /Hr,0 parameter. Where r specifies
the COM ports, r may be a single port or a range of ports. For
example:-
/H1,0 sets up DTR/CTS handshaking for COM1.
/H12,0 sets up DTR/CTS handshaking for COM12.
/H7-16,0 sets up DTR/CTS handshaking for COM7 to COM16.
RS422 Handshaking__________________
RS422 interfaces have less signals than RS232 serial ports,
but to reduce noise, while allowing high speeds and long
distance transmission, each signal is carried by two wires as a
twisted pair, and is thus a differential data transmission system.
Over distances up to 40 feet the maximum data rate is 10
Megabits per second, and for distances up to 4000 feet the
maximum data rate is 100 Kilobytes per second, allowing
communication much further and faster than RS232. Like
RS232, RS422 is usually used for data transmitted between only
one device and one other, but up to 10 devices can
simultaneously receive the transmitted data.
RS422 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 Handshake line.
CTS, Clear To Send an input to PC. Handshake line.
Chapter 1 Page 13