Atmel AVR10004: RCB256RFR2 – Hardware User Manual [APPLICATION NOTE]
10
The calibrated internal RC oscillator, pre-scaled to 8MHz, is used as the default clocking. It is recommended to use the
) clocked from the 16MHz radio reference crystal as a reference to calibrate the RC
oscillator for higher accuracy.
The symbol counter replaces and enhances the CLKM-driven timer1 function originally available in ATmega1281V-
based solutions.
A 32kHz crystal, Q1, is connected to the related Atmel ATmega256RFR2 pins (17-TOSC2; 18-TOSC1) to be used as a
low-power, real-time clock. This time base can also run in sleep mode and create timer-based system wake-up events.
4.5
On-board peripherals
4.5.1
Key and LEDs
For simple applications and debugging purposes, or just to deliver status information, a basic user interface is provided
directly on board, and consists of four LEDs and a pushbutton. Three LEDs (D2…D4) are connected to PE2…PE4 for
active-low operation. One LED (D5) signals the single-chip reset state. The pushbutton, T1, pulls PE5 to GND, and is
intended to be used in combination with the internal pull-up resistor.
When mounted on a base board, I/O ports PE4 and PE5 are used to emulate #WR and #RD lines handling a memory
interface. Therefore, the pushbutton and LED D4 are not functional. On RCB256RFR2, the port G I/O lines cannot be
used because they are shared with dedicated radio transceiver functionality.
In sleep mode, when the signals are supposed to be inactive, no additional current occurs.
Figure 4-2. RCB256RFR2 key and LED connection.
4.5.2
ID EEPROM
Firmware-based board type identification is supported by an optional identification EEPROM. Information about the
RCB itself, MAC addresses, and production calibration data are stored there. An Atmel AT25010A EEPROM
128 × 8-bit organization and SPI interface is used because of its small package, low voltage, and low-power operation.
Compared to Atmel Atmega1281V-based RCBs, the ID EEPROM interface has been designed in a different way.
Accessing the ID EEPROM requires PG5 set to logic low. This pin is not used on Atmega1281V-based RCBs (see
