Murata Electronics Corporation 11 6/2/2021
3. PROTOCOL MODES
In point-to-point applications, it is generally desired that the radios operate in a transparent
mode. That is, raw unformatted data is sent from the host to the radio and is received as raw
data from the receiving end. The addressing and error detection and correction are still
performed by the radios, but it is transparent to the user application. To set up a point-to-
point network, one radio has to be set up as a base station. When the radios are powered on,
the base station will send out the synchronization signal at the beginning of each hop. The
remote will synchronize with the base and automatically request registration. Once the
remote is registered, the radios can transmit data. Protocol mode operation is available in
point-to-point mode if desired.
If the base station is to be responsible for directing data to a specific remote in point-to-
multipoint mode, the data sent to the base station by the user application must adhere to a
packet format. This allows transmissions from the base station to be directed to a specific
remote. Data received by a base station from a remote is similarly formatted to identify to
the user application the remote that sent the transmission. The remotes may still use
transparent mode without formatting to send data to the base, if desired. The WIT2420
supports 10 protocol formats that are described in detail below. The protocol format is
selected through the Set Protocol Mode command.
Base and remote radios can use protocol modes to insure that a packet is transmitted to the
base without being broken up over multiple hops. The data length value in the data packet
becomes the effective minimum packet length and maximum packet length for that packet.
Note that if the remote data length is set to a number of bytes that is longer than the number
of bytes that can be transmitted by a remote on a single hop, the packet will be discarded. For
the base, this value is set by the Set Base Slot Size command. For remotes this value is
dynamically available through the Get Maximum Data Length command or may be
calculated based on the maximum number of remotes that can ever be registered at one time.
See Sections 5.3 and 2.2.3 respectively. Also note that using protocol modes effectively
disables Data Transmit Delay. This means that a packet will not be transmitted until the
entire packet has been sent to the radio, regardless of the amount of time it takes.
If the remote hosts can determine what data is directed to them in point-to-multipoint mode,
the data can be sent to the base station without using a packet format. In this situation,
broadcast mode is selected at the base station by using the Set Default Handle and selecting
3FH as the default handle. In this mode, the automatic retransmission of unsuccessful
transmissions is disabled. This is required since all of the remote modems will attempt to
acknowledge each base transmission when ARQ is enabled. Transmissions that are received
with errors are discarded by the radio. The remote devices must be able to detect a missing
packet and request a retransmission by the base device.
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