Ultra Low Power Operation with a Siretta NLP Modem

Applicable Products Part number Description

ZETA-NLP-LTE1 (EU) Ultra Low Power European LTE Cat 1 Modem

ZETA-NLP-LTEM (GL) Ultra Low Power Global LTE Cat M Modem

Objective Power consumption is one of the key requirements of any Wireless IoT application.

A significant contributor to power consumption in such systems is the Cellular modem.

This application note shows how to set Siretta ZETA NLP modem in ultra-low power mode for reduced energy consumption.

Solution ZETA-NLP Ultra Low Power Mode The ZETA-NLP has a special mode of operation which forces the unit to drop down to an ultra-low power state where the modem is still operational and registered on the network but is functionally asleep. This allows for the modem to remain connected to the network and be ready to send and receive data using a fraction of the energy.

This ultra-low power state is achieved by setting the following AT command to the modem:

COM3 - Tera Term VT

File Edit Setup Control Window Help

AT CFUN=5

OK

Ultra Low Power Control Signal To control the power state of the modem from low power to ultra-low power it is necessary to use a special control signal in the RS232 serial port.

The control signal is called Data Terminal Ready (DTR) and is available on the RS232 serial port on pin 4 as shown in the table below.

Once the CFUN=5 command has been issued then the modem is ready to enter ultra-low power mode. To activate low power mode and put the modem in to a dormant state the DTR line must be de-asserted on the serial port. When the device has entered ultra-low power mode the CTS line will be de-asserted indicating that the device has gone into ultra-low power state. At this point the serial port is also deactivated, and the modem will not respond to AT commands and will appear to be OFF.

To bring the modem back to normal power state and communicate with the modem again it is necessary to assert the DTR line and the modem will leave its dormant state and become fully active again for normal operation. When in the dormant ultra-low power state an incoming call request or incoming SMS will force the modem to enter its full power mode and the modem is able to be used as normal.

Pin Name Usage Status Direction

1 DCD Output from UART that indicates the carrier is present Connected OUT

2 RXD Output transmit line of UART Connected OUT

3 TXD Input receive line of UART Connected IN

4 DTR Input to UART and controls DTE ready condition Connected IN

5 GND Ground Connected IN

6 DSR Output from UART that indicates the module is ready Connected OUT

7 RTS Request to Send - Input line of UART that controls hardware flow control Connected IN

8 CTS Clear to Send - Output line of UART that controls hardware flow control Connected OUT

9 RI Ring Indicator - Output line of UART that indicates the incoming call condition Connected OUT

This mode allows the modem to consume little current whilst it is not in use but be available for use locally by asserting the DTR line. The modem power ON and power lines will remain active throughout and can also be used to turn the modem completely OFF.

DTR Control Software To control the DTR line on the modem and communicate with the AT command interface on the RS232 serial port it is necessary to use Terminal software which controls the DTR line. Siretta has tested the ZETA modem family with several terminal emulator applications which support DTR and RTS control signalling. Two recommended applications are shown below:

Realterm (Download Link)

Telit AT Controller

Ultra Low Power Receiving Data In the ultra-low power state, a special provision must be catered for when data is received from a connected socket to be output over the serial port.

In this mode it is necessary to run the serial port in the following state:

Enable hardware flow control with AT&K3

Enable low power mode by issuing AT CFUN=5

Setup a socket connection and establish an active connection

Enter ultra-low power state by de-asserting DTR control line

De-assert RTS line

Wait for specified timeout to check for incoming data

When the timeout has expired, to check for data over the connected socket follow the procedure below:

Assert DTR line to disable low power state and activate full serial port

Assert RTS line to receive full buffered data over serial port and wait for all data to be received

When all data has been received de-assert RTS line

De-assert DTR line to re-enter low power state and wait for the specified timeout to receive further data.

NOTE - While there is no data pending reception from the cellular network, the modem does meet the published low power consumption figures. However, if there is data pending from the cellular network, then the modem power consumption rises to approximately 5mA at 12V until the data transfer process has completed and low power state is re-entered. The modem does not automatically enter the full power state when there is pending cellular network data, so the connected application is required to periodically poll the cellular network. If there is pending data from the cellular network, this will immediately start to be received over the serial connection.

Once the data transfer is complete, the modem can be put back into the low power state where it will meet the published power consumption figures. The shorter the check interval, the less time will be potentially spent at the higher 5mA current consumption. The longer the check interval the less power will be used checking for received data from the network. Choose this check interval to match the requirements of your system.

Demonstration of Solution Testing Ultra Low Power Mode using an Outgoing Socket Connection COM3 - Tera Term VT

File Edit Setup Control Window Help

//Set extended error

LINK:	https://www.siretta.com/2025/03/ultra-low-power-operation-with-a-siret...
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