HopNet RS-232 Serial ModBus Radio
entire packet to come in prior to transmission start using
qd
, the Maximum Transmit
Delay (or Maximum Encapsulation Delay Command. (see Modbus Adapter
Commands) However, the downside result is higher latency. Still, this may be
desirable in situations where data integrity is paramount and higher latency can be
tolerated.
Automatic Addressing
When in Modbus mode, the HopNet radios learn the address of the Modbus device to
which they are connected. When first powered up, the base Modbus radio does not
know the Modbus address of the remote devices. When the base radio has a Modbus
packet to send, it looks at the Modbus address in the packet and then broadcasts the
packet to all of the remote radios. Only the remote radio connected to the Modbus
device whose address was specified in the Modbus packet will respond to the Modbus
packet. The base radio will store the radio ID in memory and indicate it is the radio
associated with that Modbus address. Any subsequent transmissions to that remote
Modbus device will be performed by the base radio using the radio’s addressing
scheme. This will allow the remote radio to acknowledge that data was successfully
received, improving data reliability and throughput.
If a remote Modbus device is added or removed from the wireless network, the base
radio will learn and remember that information on the fly without the need to reset the
network. This provides the utmost flexibility in installing and changing the wireless
network.
DNP3/DF1 Operation
DNP3 protocol is supported by the HN210D adapter in Transparent mode. Point to
multipoint configurations of DNP3 are supported however, peer-to-peer are not.
Occasionally, the device receiving DNP3 has a packet timeout that will reject any
packet with relatively large gaps between bytes. If this occurs, Adapter Command
QP2 (Encapsulation Mode) is required with QD being set to the proper size to fully
insure that the packet comes through without gaps.
QD = (# milliseconds of LEP [Largest Expected Packet] / 3ms
# milliseconds of LEP = 8000 * (expected number bytes) / (baud rate)
DF1 in half-duplex mode is supported by the adapter in QP0 (Transparent Mode).
However, as above, if the device has a packet timeout, QP2 may be required. Peer-
to-peer is supported in that DF1 already supports peer-to-peer by sending the message
to the master and having it resend the packet formatted for the receiving remote. DF1
in full-duplex mode is not supported.
Note: The HN210D radio must be in broadcast mode in order to use both the DNP3
and DF1 protocols.
©
2000- 2004 Cirronet
™
Inc
33
M-2410-0022 Rev B
