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7000 Bus Converter User Manual (version 1.2,Feb/2003, 7PH-006-10) --------------- 10
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 signal 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
PLC use 11-bit data format and some weight scale equipment uses 12-
bit. If the host-PC has to send command to remote modules, PLC and
weight scale equipment, one possibility is to use three independent
two-wire RS-485 networks. However, this may increase the system
cost and reduced the system reliability.
An other option for the user is to use many modules in the same two-
wire RS-485 network for real world applications. All these modules
must communicate at the same baud rate in a conventional system.
Some of those modules may be very close to the host-PC and will be
able to communicate at a high baud rate. Some modules may be far
away from the host-PC and will communicate at a low baud rate.
Because only one speed is valid in the RS-485 network, the high-speed
modules should be forced to communicate at a low speed baud rate.
In
other words, the performance of the whole system should be decreased.
The 7000 Series RS-485 Network: The 7000 RS-485 network is the
most powerful and flexible two-wire RS-485 network 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.