ICP DAS USA 7000 Series User Manual page 8

Conventional Two-Wire RS-485 Network: The conventional two-wire RS-
485 network uses a DIP SWITCH selectable converter to convert host
RS-232 or USB signals to a two-wire RS-485 signal. The baud rate and
data format must be set to a fixed value for the whole network. For
example, the user can choose baud rate=9600 and data format=10 bit per
character. This limitation is inconvenient for some real world applications.
The 7000 series, Adam 4000 series, Nudam 6000 series and
DATAFORTH 9B series all use a 10-bit format. Some conventional PLCs
use an 11-bit data format and some weight scale equipment uses 12-bit. If
the host-PC needs to send commands to remote modules, PLCs and
weight scale equipment, one possibility is to use three independent two-
wire RS-485 networks. However, this may increase system cost and
reduce system reliability.
Another option for real world applications is to use many modules in the
same two-wire RS-485 network. Each module must communicate at the
same baud rate in a conventional system. Some module may be very
close to the host-PC and will be able to communicate at a higher baud
rate. Other modules may be farther away from the host-PC and will
communicate at a lower baud rate. Since only one speed is valid in an
RS-485 network, the higher speed modules should be forced to
communicate at a lower speed baud rate. In other words, the
performance of the entire system must be decreased.
The 7000 Series RS-485 Network: The 7000 RS-485 network is the
most powerful and flexible two-wire RS-485 networks in the world. It is
a multiple baud rate and multiple data format network system. That is to
say, all the remote modules mentioned above, PLCs and weight scale
equipment share the same RS-485 network. The 7520, RS-232 to RS-
485 converter, equips a "Self Tuner" inside, therefore it can detect the
baud rate and data format automatically and control the direction of the
RS-485 network precisely. Therefore the user can connect all this
equipment to the same RS-485 network. This method will greatly
reduce system cost and increase reliability.
7000 Bus Converter User's Manual (Version 1.8 Jan/2006, 7PH-006-18) --------------- 8