Linx Technologies TRM-915-R250 - Manual (Page 8)

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Low-Power States
The module supports three power saving modes: Standby, Sleep and Deep
Sleep. Standby and Sleep are included primarily for legacy compatibility
with DTS and EUR Series modules. The hardware required to support
these two low-power modes fully is not present in the 25 Series modules.
As a result, the current consumption in these two modes is considerably
higher than their DTS / EUR counterparts. It is recommended that
applications utilize the Deep Sleep mode for power savings.
In the Sleep and Deep Sleep modes, the transceiver is powered down
and does not synchronize with other modules. Sleep mode draws more
current than Deep Sleep mode. In Deep Sleep mode the module draws the
least current. To wake the module up from this mode the RESET line must
be held low for at least 20µs and then taken high. The module does not
monitor the receive channel in either mode. Therefore, a sleeping module
cannot be woken through the RF interface.
If regACKONWAKE is enabled, the module transmits a 0x06 character on
the TXD line once awakened from a low-power mode or power-off state.
This indicates that the module is ready to resume operations.
Figure 8 indicates the line states while in a low-power mode.
250 Series Transceiver Low-Power Line States
Line Name Pin Number Pin State
PR_PKT 1 Driven low
TXD 2 Input with weak pull-up
RESET 6 Input with weak pull-up
C2D 7 Input with weak pull-up
CMD_RSP 9 Input with weak pull-up
EX 10 Driven low
RSSI 14 Driven low
CMD 15 Input with weak pull-up
BE 16 Input with weak pull-up
CTS 19 In Standby, Sleep: Driven Low, In Deep Sleep: Driven High
RXD 20 Input with weak pull-up
Figure 8: 250 Series Transceiver Low-Power Line States
Standby
Standby is selected by writing a 0x02 to regOPMODE. In this mode,
the internal oscillator of the module’s protocol controller is lowered to its
slowest setting. The transmitter and receiver hardware is in power-down,
but the radio’s oscillator is enabled and running. The module wakes from
standby in less than 6ms. A low pulse on the RXD line wakes the module.
This pulse should be at least 1 bit-time in duration, so sending any byte to
the UART wakes it with the low start bit. Because the module’s oscillator
is not capable at running at ultra-low speeds, use of this mode is not
recommended for new applications. The RAM contents are preserved
during standby. If the RAM fails an integrity check, the module issues itself
a software reset to force re-initialization.
Sleep
Sleep is selected by writing a 0x01 to regOPMODE. The internal oscillator
of the module’s protocol controller is lowered to its slowest setting, and
all radio services are stopped (receiver, transmitter, oscillator, etc.). The
module wakes from sleep in less than 6ms. A low pulse on the RXD line
wakes the module. This pulse should be at least 1 bit-time in duration, so
sending any byte to the UART wakes it with the low start bit. Because the
module’s oscillator is not capable at running at ultra-low speeds, use of
this mode is not recommended for new applications. The RAM contents
are preserved during sleep. If the RAM fails an integrity check, the module
issues itself a software reset to force re-initialization.
Deep Sleep
Deep sleep is selected by writing a 0x03 to regOPMODE. When the
module is put into deep sleep, the CTS line is brought high to indicate that
the module is not ready to accept UART data. The radio is placed in its
lowest power mode and all services are stopped. The protocol controller’s
oscillator is also stopped and all non-essential functions are turned off.
While powered, this mode consumes the least amount of current. The
module wakes from deep sleep in less than 6ms. A low pulse of at least
20µs on the RESET line starts the waking process, but the module doesn’t
begin executing wake instructions until the RESET line is returned high.
As with the other low-power modes, the RAM contents are preserved.
If the RAM fails an integrity check, the module issues itself a software
reset to force re-initialization. Note that, if the volatile data rate register is
changed during the host application initialization (regUARTDATARATE),
the re-initialization returns the module to the value in the non-volatile
counterpart (regNVUSERDATARATE).