User's Manual

Atmel AVR2080
3
8479A-AVR-01/12
4 Functional description
The block diagram of the Atmel REB231FE2 radio extender board is shown in Figure
4-1. The power supply pins and all digital I/Os of the radio transceiver are routed to
the 2 × 20-pin expansion connector to interface to a power supply and a
microcontroller.
The Atmel AT86RF231 antenna diversity (AD) feature supports the control of two
antennas (ANT0/ANT1). A digital control pin (DIG1) is used to control an external RF
switch selecting one of the two antennas. During the RX listening period, the radio
transceiver switches between the two antennas autonomously, without the need for
microcontroller interaction, if the AD algorithm is enabled. Once an IEEE 802.15.4
synchronization header is detected, an antenna providing sufficient signal quality is
selected to receive the remaining frame. This ensures reliability and robustness,
especially in harsh environments with strong multipath fading effects.
Board-specific information such as board identifier, the node MAC address, and
production calibration values are stored in an ID EEPROM. The SPI bus of the
EEPROM is shared with the radio transceiver’s interface.
Figure 4-1. REB231FE2 block diagram.
AT86RF231
RFP
RFN
DIG2
EXPAND1
SE2431L
ANT2
ANT1
XTAL2 XTAL1
XTAL
DIG1
CLKM
Protection
VDD
VSS
ID
EEPROM
SPI
4
IRQ
RSTN
SLPTR
DIG4
DIG3
DIG2
TP6
50R
TP7
LPF
LPF
VDD
VDD
X2
X3
4.1 Interface connector specification
The REB is equipped with a 2 × 20-pin, 100mil expansion connector. The pin
assignment enables a direct interface to the REB-CBB [2]. Further, the i
nterface
connects to the Atmel STK
®
500/501 microcontroller development platform to enable
support for various Atmel 8-bit AVR
®
microcontrollers.
The REB is preconfigured to interface to the REB-CBB and STK501 with an Atmel
ATmega1281.
If an Atmel ATmega644 is used as the microcontroller, the 0 resistors R10 through
R18 must be removed and re-installed on the board manually as resistors R20
through R28 (see appendix A.1).
Other mi
crocontroller development platforms need to be interfaced using dedicated
adapter boards.