Rainbow Electronics ATmega128RFA1 - Manual (Page 79)

79
8266A-MCU Wireless-12/09
ATmega128RFA1
The PHR and the PSDU need to be stored in the Frame Buffer for frame transmission.
The PHR byte is the first byte in the Frame Buffer (address 0x180) and must be
calculated based on the PHR and the PSDU. The maximum frame size supported by
the radio transceiver is 128 bytes. If the TX_AUTO_CRC_ON bit is set in register
PHY_TX_PWR, the FCS field of the PSDU is replaced by the automatically calculated
FCS during frame transmission. There is no need to write the FCS field when using the
automatic FCS generation.
Manipulating individual bytes of the Frame Buffer is simply possible by accessing the
appropriate buffer address.
The minimum frame length supported by the radio transceiver for non IEEE 802.15.4
compliant frames is one byte (Frame Length Field + 1 byte of data).
9.6.4 Battery Monitor (BATMON)
The main features of the battery monitor are:
• Configurable voltage threshold range from 1.7V to 3.675V
• Generates an interrupt when supply voltage drops below the threshold
9.6.4.1 Overview
The battery monitor (BATMON) detects and indicates a low supply voltage of EVDD.
This is done by comparing the voltage of EVDD with a configurable, internal threshold
voltage. A simplified schematic of the BATMON with the most important input and
output signals is shown in the following figure.
Figure 9-24. Simplified Schematic of BATMON
BATMON_HR
BATMON_VTH
4
EVDD
Threshold
Voltage
BATMON_OK
„1“
BATMON_IRQ
For input-to-output mapping
see BATMON register
DAC
+
-
D
Q
clear
9.6.4.2 Configuration
The Battery Monitor can be configured using the BATMON register. Register subfield
BATMON_VTH sets the threshold voltage. It is configurable with a resolution of 75 mV
in the upper voltage range (BATMON_HR = 1) and with a resolution of 50 mV in the
lower voltage range (BATMON_HR = 0).
9.6.4.3 Data Interpretation
The bit BATMON_OK of register BATMON monitors the current value of the battery
voltage:
• If BATMON_OK = 0 then the battery voltage is lower than the threshold voltage;
• If BATMON_OK = 1 then the battery voltage is higher than the threshold voltage;