Analog Devices UG-065 Evaluation Board User Guide, Overview, RESET/PROG Push-Buttons, Firmware

Evaluation Board User Guide UG-065

OVERVIEW

The ADXL345 inertial sensor development board has the following features:

•A 2-layer printed circuit board (PCB), 1.125-inches × 2.25- inches form factor

•A two AAA battery power supply

•A 4-pin UART header to connect to RS232 interface cable

•Reset/download push-buttons

•Power indicator/general-purpose LEDs

•Access to all microcontroller I/Os from the external header; all device pins are brought out to the external header pins

•Demonstration firmware

RESET/PROG Push-Buttons

A RESET push-button is provided to allow the user to manually reset the part. When inserted, the RESET pin of the ADuC7024 is pulled to GND. Because the RESET pin on the ADuC7024 is Schmitt-triggered internally, there is no need to use an external Schmitt trigger on this pin.

To enter serial download mode, the user must hold the P0.0/BM pin low while reset is toggled. On the development board, serial download mode can be easily initiated by holding down the serial download push-button (PROG) while inserting and releasing the reset button (RESET), as illustrated in Figure 2.

FEATURES

Power Supply

A pair of AAA batteries powers the board, and the battery holder is located on the back of the board. An on/off switch on the lower left of the front of the board controls power to it. The battery voltage is not regulated but is decoupled with a 10 µF capacitor globally, and an additional 1 µF capacitor at the device supply pins to ground.

RS232 Interface

The ADuC7024 (UC1) P1.1 and P1.0 lines are connected to the RS232 interface cable via the connector (UART). The interface cable generates the required level shifting to allow direct connection to a PC serial port. Ensure that the supplied cable is connected to the board correctly, that is, VDD is connected to VDD and GND is connected to GND.

Power Indicator/General-Purpose LEDs

Two general-purpose LEDs are available on the board. A red LED (LED1) is connected to P4.5 of the ADuC7024, and a green LED (LED2) is connected to P4.4. Both LEDs can be repurposed via firmware.

Breakout Header

All ADuC7024 pins are brought out to headers on either side of the board. The headers come unpopulated but can be populated using standard 0.1-inch header pins.

The thin form factor of the top of the board allows the design of an expansion board to connect above the development board, with the header pins providing both electrical and physical connections.

Firmware

Sample firmware is provided on the ADXL345 product page.

(A) RESET AND PROG RELEASED (B) PUSH PROG (C) PUSH RESET

RESET	PROG	RESET	PROG	RESET	PROG
	(D) RELEASE RESET		(E) RELEASE PROG

RESET PROG RESET PROG

Figure 2. Entering Serial Download Mode to Reprogram the Board

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