AT43USB326 datasheet(40/102 Pages) ATMEL

40 / 102 page

AT43USB326

3313D–USB–04/06

In the same operation, write a logical one to WDTOE and WDE. A logical one must be

written to WDE even though it is set to one before the disable operation starts.

Within the next four clock cycles, write a logical 0 to WDE. This disables the watchdog.

• Bits 2..0 – WDP2, WDP1, WDP0: Watch Dog Timer Prescaler 2, 1 and 0

The WDP2, WDP1 and WDP0 bits determine the Watchdog Timer prescaling when the

Watchdog Timer is enabled. The different prescaling values and their corresponding Time-out

Periods are shown in Table 11.

Note:

The WDR (Watchdog Reset) instruction should always be executed before the Watchdog Timer

is enabled. This ensures that the reset period will be in accordance with the Watchdog Timer

prescale settings. If the Watchdog Timer is enabled without reset, the watchdog timer may not

start to count from zero. To avoid unintentional MCU reset, the Watchdog Timer should be dis-

abled or reset before changing the Watchdog Timer Prescale Select.

I/O Ports

All AVR ports have true Read-Modify-Write functionality when used as general digital I/O

ports. This means that the direction of one port pin can be changed without unintentionally

changing the direction of any other pin with the SBI and CBI instructions. The same applies for

changing drive value if configured as output or enabling/disabling of pull-up resistors if config-

ured as input.

The keyboard matrix strobe output pins, PA[0:7], PB[0:7] and PE[0:1] have controlled slope

drivers. With a load of 100 pF, the output fall time ranges between 75 ns and 300 ns. The key-

board matrix strobe input pins, PC[0:7] have built-in pull-up resistors, 20 K

Ω nominal value, to

the internal 3.3V power supply.

PE[4:7] have 5V tolerant outputs and each has a built-in series resistor of 330

Ω nominal value.

These output pins are designed for driving an LED connected to the 5V supply.

The dedicated functions are summarized in Table 12.

Table 11. Watchdog Timer Prescale Select

WDP2

WDP1

WDP0

Number of WDT Oscillator cycles

Time-out

8K cycles

8.2 ms

16K cycles

16.4 ms

32K cycles

33.8 ms

64K cycles

65.6 ms

128K cycles

0.131 s

256K cycles

0.262 s

512K cycles

0.524 s

1,024K cycles

1.048 s

Table 12. GPIO Function Assignments

Function

GPIO

Scan out[0:7]

PA[0:7]

Scan out[8:15]

PB[0:7]

Scan out[16,17]

PE[0,1]

Scan in[0:7]

PC[0:7]

LED drivers

PE[4:7]

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