2.1
DNT90M Addressing
Each DNT90M has a unique three-byte
MAC address
, which is used to send unicast packets to it. A DNT90M can also
send a packet to all other DNT90M’s in its network by using the broadcast address 0xFFFFFF. The MAC address can be
read or bar-code scanned from the label on top of each DNT90M radio, or retrieved through the radio’s serial port or SPI
interface. There are four sources of destination MAC addresses a DNT90M can use when sending a packet:
- the broadcast MAC address, 0xFFFFFF
- the MAC address in the transparent mode destination address
(RmtTransDestAddr)
parameter
- the MAC address included in a protocol-formatted message from the DNT90M’s host
- the MAC address of the originator of the most recent packet received, when the
TransPtTo-
PtMode
parameter is enabled.
Parameters related to MAC address selection are discussed in detail in Section 7.4 of this document.
All DNT90M radios hold a
system ID
parameter that can be used to distinguish between overlapping DNT90M networks.
System IDs provide network filtering for broadcast packets. Also, a unique frequency hopping pattern is associated with
each of the 64 available system IDs, minimizing the chances of transmission collisions between overlapping DNT90M
networks.
2.2
DN24M Transmission Error Control
DNT90M packets include 24 error detection bits, allowing the integrity of a received packet to be tested with very high
confidence. A received packet is discarded if an error is detected. Error-free unicast packets are acknowledged by an
ACK message back to the originator from the destination radio. If the originator does not receive an ACK for a transmitted
packet, it will resend it on the next channel in the frequency hop sequence, etc., up to a limit set by the
ArqAttemptLimit
parameter. The default value for this parameter is 10 attempts, which ensures message delivery in all but the most ex-
treme conditions.
The number of times a broadcast packet is sent is controlled by the
BcstAttemptLimit
parameter. The radio moves to the
next channel in the hopping sequence after each broadcast transmission to mitigate the chances of a reception error due
to poor propagation or interference on one channel. The default value of the
BcstAttemptLimit
parameter is four.
To manage transmission collisions between multiple DNT90M radios trying to transmit at the same time, a progressive
random delay is used to offset the time an unacknowledged packet is retransmitted as a radio progresses through the
network’s hopping sequence.
2.3
Transparent and Protocol-formatted Serial Data
A DNT90M can directly input and output data bytes and data strings on its serial port. This is referred to as
transparent
serial port operation. DNT90M radios also support
protocol-formatted messages
, which can also be used to carry data
bytes and data strings, and must be used for:
- configuration commands and replies
- I/O event messages
- announcement messages including heartbeats
©2012 by Murata Electronics N.A., Inc.
DNT90M Integration Guide (2012/09/17)
Page 10 of 74
www.murata.com
