HopNet RS-232 Serial ModBus Radio
message. If a reply is required, the controller will construct the reply message and
send it using Modbus protocol.
This conversion also extends to resolving node addresses, routing paths, and error–
checking methods specific to each kind of network. For example, Modbus device
addresses contained in the Modbus protocol will be converted into node addresses
prior to transmission of the messages. Error–checking fields will also be applied to
message packets, consistent with each network’s protocol. At the final point of
delivery, however – for example, a controller – the contents of the imbedded
message, written using Modbus protocol, define the action to be taken.
DNP3
DNP3 is a protocol for transmission of data from point A to point B using serial
communications. It has been used primarily by utilities like the electric companies,
but it operates suitably in other areas. DNP3 is a non-proprietary protocol that is
available worldwide with no restrictions.
The DNP3 protocol allows a server to send binary input data that is useful to monitor
two-state devices. For example a circuit breaker that is closed/tripped or a pipeline
pressure alarm that shows normal or excessive pressure would both be types of binary
data sent by the server. It also allows a server to send analog input data that conveys
information like voltages, currents, power, reservoir water levels and temperatures. In
addition, it allows the sending of count input data and finally, it allows the sending of
files that contain configuration data.
The DNP3 protocol allows a client to issue control commands. For example, to close
or trip a circuit breaker, raise or lower a gate, and open or close a valve. It could also
allow the sending of analog output values to set a regulated pressure or set a desired
voltage level. It also would allow computers to talk to each other about synchronizing
the time and date, sending historical or logged data and waveform data.
DNP3 was designed to optimize the transmission of data acquisition information and
control commands from one computer to another. It is not a general purpose protocol
for transmitting hypertext, multimedia or huge files. The terms server and client are
applicable to DNP3 systems. A server is a device or software process that has data or
information that someone else wants. A client is a device or software process that
requests data from a server.
DF1
DF1 protocol is a proprietary data-link layer protocol that combines features of
subcategories D1 (data transparency) and F1 (two-way simultaneous transmission
with embedded responses) of ANSI x3.28 specification. There are two categories of
DF1 protocol, half-duplex protocol and full-duplex protocol.
A link protocol is a set of programming rules for interpreting the signals transmitted
over a physical link. The DF1 protocol carries a message, error free, from one end of
the link to the other. It has no concern for the content of the message, the function of
the message, or the ultimate purpose of the message. For example, with full-duplex
DF1 protocol, it accomplishes this by attaching a check character (BCC) or check
characters (CRC) to the end of each command and reply. The device receiving the
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