Murata WIT2420 - Low Power Mode and Duty Cycling; RF Flow Control Mode

Murata Electronics Corporation 10 6/2/2021
2.3.3. Low Power Mode and Duty Cycling
To conserve power, WIT2420 remotes power down the receiver and transmitter between
hops when not in use. Base stations must remain active all the time to handle any
transmission from any remote. Remotes can save even more power by enabling the duty
cycle feature. This feature causes a remote to power down for 2
N
frequency hops where 1/2
N
is the duty cycle. Rather than attempting to transmit on every frequency hop when data is in
the transmit buffer, a remote will attempt to transmit only every 2
N
hops. Roughly speaking,
this will proportionately reduce the average power consumption while increasing average
latency. When there are more than 16 remotes being operated in TDMA mode, duty cycling
must be enabled since a maximum of 16 time slots is available per hop.
2.3.4. RF Flow Control Mode
Because of slight differences in baud rates between transmitting and receiving hosts, when
sending large amounts of data (100’s of KB) in one direction in a point-to-point application,
it is possible to overrun the receive buffer of the receiving radio. For example a nominal
115.2Kbaud at the transmitting radio’s host might really be 115,201 and at the receiving
radio’s host it might be 115,199. This is similar to a situation where the transmitting radio is
sent data at a higher baud rate than the baud rate at which data is received by the receiving
host. To compensate for the variations in nominal baud rates, the WIT2420 supports an RF
flow control mode for point-to-point operation. In this mode, when the receive buffer of the
receiving WIT2420 is close to full, the receiving WIT2420 stops acknowledging
transmissions. The transmitting radio is set to infinite retries which invokes the RF flow
control mode (See Set Packet Attempts Limit in Section 5.3). The receiving radio will not
begin acknowledging transmissions from the transmitting radio until more room in the
receive buffer has become available. This will cause data in the transmit buffer of the
transmitting radio to back up. If it backs up to the point where the transmit buffer fills up, the
transmitting radio will deassert CTS stopping data from the transmitting radio’s host device.
Once room is available in the receiving radio’s buffer, the receiving radio will begin
acknowledging transmissions from the transmitting radio allowing the transmitting radio’s
buffer to begin to empty which will cause the transmitting radio to reassert CTS. Either one
or both of the radios in a point-to-point installation can be configured for the RF flow
control. If this mode is invoked in a point-to-multipoint installation, communications with all
radios will be stopped when any one radio’s receive buffer becomes full.