10

Atmel AVR1923

8394B-AVR-02/12

to measure the backup system power consumption a header with a mounted jumper

is available. The header is shown in Figure 3-1 and is also marked with “VBAT” on

the silkscreen. The jumper can also be used to simulate battery insertion and removal

without actually removing the battery from the holder.

5.4 Mechanical buttons

Three mechanical buttons are connected to Atmel AVR XMEGA. All buttons have

external pull-ups so there is no need to activate internal pull-ups in order to use them.

When a button is pressed it will drive the I/O line to GND.

Table 5-4. Mechanical button connection.

Pin on XMEGA

Silkscreen text on PCB and designator in the schematics

PE5

SW0

PF1

SW1

PF2

SW2

5.5 LEDs

There are four LEDs available on the board that can be turned on and off. Two yellow

LEDs, one green LED (power indicator LED), and one red LED (status LED). The

green and red LEDs are inside the same package and therefore the colors can be

mixed to orange when both are activated. The yellow LEDs and the red LED can be

activated by driving the connected I/O line to GND. The green LED is controlled via a

FET and is by default on when the board is powered. However, this power indicator

LED can also be turned off by driving the gate of the FET to GND.

Table 5-5. LED connections.

Pin on XMEGA

LED

PR0

Yellow LED0

PR1

Yellow LED1

PD4

Red status LED

PD5

Green power indicator LED

5.6 FSTN LCD display

The NHD-C12832A1Z-FSW-FBW-3V3 is a FSTN LCD display and has a resolution of

128 x 32 pixels. In the design the display is connected via a SPI based interface.

Detailed information about the display can be obtained from the display datasheet

(NHD-C12832A1Z-FSW-FBW-3V3 from New Haven Displays) and from the display

controller datasheet (ST7565R from Sitronix).

The external circuitry of the display is configured to boost the 3.3V supply voltage by

a factor of 3 to ~10V. However, the typical supply voltage of the display (contrast

control) is 6V and therefore the boosted supply must be adjusted, and this must be

done by software when the display is configured. The following formula is used when

the voltage is adjusted by software:

REG

V

Ra

Rb

V

⋅

⎟

⎠

⎞

⎜

⎝

⎛ −

⋅

⎟

⎠

⎞

⎜

⎝

⎛ +

=

162

1

1

0

α