Wi reless M-Bus-EK

Rev. 0.1

9

8.5. Data Select

The options for the Data Select menu are:

The selected data is displayed on the LCD and transmitted in the data payload.

The Pulse option provides a pulse counter. The C8051F342 acts as a virtual water or gas meter. The C8051F930

will wake up on each rising and falling edge and count the number of pulses. The pulse rate is programmable.

The Temperature sensor uses the onboard temperature sensor on the C8051F930.

The power consumption will be higher using the pulse counter. This is because the MCU must wake up often to

count the number of pulses. Using the temperature sensor, the current consumption is less because the

temperature is only measured before each transmission.

8.6. Pulse Frequency

When pulse data is selected, the pulse frequency is programmable from 0.1 to 10 Hz. The 0.1 Hz provides one

pulse every ten seconds.

8.7. Encryption

The AES encryption option will encrypt the data before sending. The demo uses the AES 128 block cipher.

Ecrypting the data takes some extra time and results in higher power consumption. The encryption time will be

higher for longer data lengths.

Since the demo uses the basic AES128 block cypher, the data size must be a multiple of 16. The transmission data

should be padded with zeros. Other encryption modes might accommodate an arbitrary length.

8.8. LCD enabled

The LCD display takes power to operate and update. The three-pin header, J9, may be configured to exclude the

LCD current from the measurement. However, the C8051F930 is still updating the LCD display. Disabling the LCD

turns off the Meter display, and the MCU will not have to update the display. This decreases the time that the

C8051F930 has to be awake and lowers power consumption.

Normally, the CP2400 is powered from the same voltage supply as the C8051F930. However, the LCD current is

so low that the CP2400 may be powered from an I/O pin of the C8051F930. The LCD current may be further

decreased by configuring J13 with a shorting block on Pins 1 and 2. This powers the CP2400 from an C8051F930

I/O pin and further lowers the power consumption when the LCD is disabled.