M-2911 BlueJay Wireless Data Transceiver
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Generally, the other parameters (Baud Rate, Data Bits, Parity, Packet Size, Time-out, etc.) would be
identical, though there are instances when this would not be the case. Those instances will be explained in
greater detail later on in this section.
Another M-2911 application would be to configure a "Network" of units, where a Master unit polls several
Slave units. This would be the case where there is a Data Collection unit communicating with several IED’s.
In this case, the Multicast Address would be used to allow one unit to communicate with several others
simultaneously. For this example, the Master Unit would be set with a normal Unit Address (1-250), which is
the address the Slave units would use for their Destination Address. The Master unit would have a
Destination Address between 251 and 254, which are the "Multicast Addresses". These addresses are
distinct in that transmissions sent to these addresses are not acknowledged by the receiving M-2911, which
allows data to be sent to many Slave units without causing data clashes since these Slave units do not
attempt to acknowledge the Master units transmission. The Slave units would all have their Multicast
Address set to the selected Multicast Address (251-254), while their Destination Address would all be set to
the Master units address (1-250). They would each be given a separate Unit Address (1-250) different from
the Master unit and other Slave units.
For this application, data sent from the Master unit would be passed out to all Slave units (to the individual
IEDs) simultaneously, while response data from a Slave unit would be passed back to the Master unit (to the
RTU).
For this application, the data transfers must involve a protocol where each Slave unit can be addressed
individually within the data transferred to all units, such that only one of the Slave units at a given time will
accept, and respond to, the data.
Address 255 is a special case in that all units within the range of transmission of a unit set to Destination
Address 255 will receive these transmissions, no matter what their Unit or Multicast Address is. This is the
"Broadcast Address", and is used for system-wide commands, for example Load Reduction commands. In
this case also, units receiving data with this Broadcast Address will not attempt to acknowledge this
transmission.
Baud Rate:
ATB=nnnnnn
4800, 9600, 14400, 19200, 28800, 38400, 57600, 76800, 115200
Generally M-2911s that communicate with each other would have the same baud rate, as dictated by the
equipment to which they are attached.
The baud rate is selectable between 4800 and 115,200 bits per second (bps), over the standard baud rates:
4800, 9600, 14400, 19200, 28800, 38400, 57600, 76800, and 115200.
In some applications, IEDs in a system may not have equal baud rates, and in some instances, the M-2911
can be used to convert between these baud rates. The limitation of converting between baud rates is that the
data transferred must be in packets of less than 128 bytes (including packet overhead such as addresses
and checksums, etc.), as this is the size of the data buffer within the M-2911. If data is transferred in such
packets, and the protocol waits for acknowledgment (or response) to each packet, the M-2911 will provide for
baud-rate conversion over their operating range (4800-115200 bps). In such a situation, data will flow into the
faster-set unit in less time than it flows out of the slower-set unit, and communication speed will be limited to
the rate of the slower unit. For this application, the receive time-outs in the protocol must be configured to
tolerate the slower rate.
Parity:
ATP=x
E, O, N (Even, Odd, None)
Most IEDs no longer use Parity (an extra bit added to each character to serve as a simple checksum), and
send just the eight data bits preceded by a Start Bit and are followed by a Stop Bit. For these IEDs, the Parity
is set to NONE.
For those devices that still utilize parity, the M-2911 should be set with the same parity – EVEN or ODD.
Even parity is where the appended parity bit serves to keep the total number of ‘1’ bits in the data and parity
an even number (if the data has an odd number of "1" bits the parity bit is set to "1", if the data has an even
number of "1" bits the parity bit is set to ‘0’).
