Murata Electronics Corporation 6 6/2/2021
specified delay is exceeded before transmitting. If the remote has more data than can be sent
on one hop, it will send as much data as possible as a packet, adding its own address, a
packet sequence number and 24-bit CRC. These additional bytes are transparent to the user
application if the protocol mode is 00 (which is the default). In the event a remote has more
data to send, the data will be sent on subsequent hops. If the transmission is received by the
base station without errors, the base station will acknowledge the transmission. If the remote
does not receive an acknowledgment, it will retransmit the data on the next frequency hop.
To the user application, acknowledgments and retransmissions all take place behind the
scenes without the need for user intervention.
2.2.2. Point-to-Multipoint
In point-to-multipoint mode, data sent from the user application to the base station must be
packetized by the user application unless the remote device can distinguish between
transmissions intended for it and transmissions intended for other remote devices. This is
necessary to identify the remote to which the base station should send data. When the user
packet is received by the remote, if the remote is in transparent mode (protocol mode 0), the
packetization bytes are stripped by the remote. In this instance the remote host receives just
data. If the remote is not in transparent mode, the remote host will receive the appropriate
packet header as specified by the remote’s protocol mode. Refer to the section Protocol
Modes for details on the various packet formats.
When a remote sends data to a base station in point-to-multipoint mode, the remote host does
not need to perform any packetization of the data. Remotes can operate in transparent mode
even though the base is operating in a packet mode. The remote will add address, sequence
and CRC bytes as in the point-to-point mode. When the base station receives the data, the
base station will add packetization header bytes according to its protocol mode setting.
2.2.3. TDMA Mode
For applications needing guaranteed bandwidth availability, the TDMA mode of the
WIT2420 can meet this requirement. In TDMA mode, each remote has an assigned time slot
during which it can transmit. The base station time slot is set independently of the remote
time slots through the Set Base Slot Size command. The base station assigns each remote a
time slot and informs the remotes of the size of the time slot. All remote time slots are the
same size that is determined by the number of remotes registered with the base station. The
slot size is a dynamic variable that changes as the number of registered remotes changes.
The remotes are continually updated with the time slot size. This approach continually
maximizes the data throughput. The base station divides the amount of time available per
hop by the number of registered remotes up to a maximum of 16 times slots per hop. If the
number of registered remotes is greater than 16, the time slots will be spread across the
required number of hops. For networks with more than 16 possible remotes, the Set Duty
Cycle command must be used to specify a duty cycle -- the number of hops over which the
time slots must be spread. For 1 to 16 remotes, no duty cycle is required; for 17 to 32
remotes a duty cycle of at least ½ is required; and for 33 to 62 remotes a duty cycle of ¼ or
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