Murata Electronics Corporation 9 6/2/2021
All of this error detection and correction is transparent to the user application. All the user
application sees is error-free data from the modem. However, if the ARQ mode is disabled,
transmissions with errors are discarded, and missing data detection will be the responsibility
of the user application. Refer to the Protocol Commands section for complete details.
2.3. Modes of Operation
2.3.1. Control and Data Modes
The WIT2420 has two modes of operation: Control mode and Data mode. When in Control
Mode, the various radio and modem parameters can be modified. When in Data Mode, only
data can be transmitted. The default mode is Data Mode. There are two ways to enter
Control Mode. The first way is to assert the Configure (CFG) pin on the modem. Upon
entering Control Mode, the modem will respond with a > prompt. After each command is
entered, the modem will again respond with a > prompt. As long as the CFG pin is asserted,
data sent to the modem will be interpreted as command data. Once the CFG pin is
deasserted, the modem will return to Data Mode.
The second method for entering Control Mode is to send the escape sequence :WIT2420 (all
lower case) followed by a carriage return. In the default mode, the escape sequence is only
valid immediately after power up or after deassertion of the Sleep pin on the modem. The
modem will respond in the same way with a > prompt. To return to Data Mode, enter the
Exit Modem Control Mode command, z>, or assert and deassert the Sleep pin. There are
three modes for the escape sequence, controlled by the Set Escape Sequence Mode command,
zc:
zc = 0 Escape sequence disabled
zc = 1 Escape sequence available once at startup (default setting)
zc = 2 Escape sequence available at any time
The zc2 mode setting is useful if the user application has a need to change the modem
settings "on the fly". In this mode the escape sequence is always enabled and may be sent at
any time after a pause of at least 20ms. The modem will respond in the same way as when in
the default mode. It is necessary to issue the Exit Modem Control Mode command, z>, before
resuming data transmission. The escape sequence must be interpreted as data until the last
character is received and as such may be transmitted by the modem to any listening modems.
2.3.2. Sleep Mode
To save power consumption for intermittent transmit applications, the WIT2420 supports a
Sleep Mode. Sleep Mode is entered by asserting the Sleep pin on the modem interface.
While in Sleep Mode, the modem consumes less than 50µA. This mode allows the radio to
be powered off while the terminal device remains powered. After leaving Sleep Mode, the
radio must re-synchronize with the base station and re-register.
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