AT91SAM7A2-AI datasheet(64/369 Pages) ATMEL

64 / 369 page

PRELIMINARY

AT91SAM7A2

6021A–ATARM–07/04

When the counter reaches 0, it triggers the programmed action (internal reset or

interrupt).

If no WD reset is programmed (i.e. RSTEN is at a logical 0) when the WD reaches 0, it is

reset to the programmed value and continues to count, unless it is disabled. This

enables it to be used to generate periodic interrupts.

Block Diagram

Figure 41. Watchdog Block Diagram

Internal Reset Pulse

Generation

If the RSTEN bit is set in the WD_OMR register, an internal reset pulse is generated

when the overflow occurs. This pulse is 8 clock cycles long (CORECLK) and is not

affected by hardware reset.

After a reset (hardware or WD), the clock selected by the watchdog is LFCLK/2.

Internal Interrupt Request

The watchdog can generate an internal interrupt request when an overflow occurs. The

software can enable or disable this interrupt either in the WD module (WD_IMR register)

or in the GIC registers.

Example

The LFCLK clock source from the clock manager is used to select the WDSCLK.

The following example uses LFCLK as a value of 32.768 kHz and a pending window of

0xFF.

Example use of the Watchdog

Use of the Pending Window to generate an interrupt and reload the watchdog counter

within the window only.

PWL[15:0]

()

WDCLK

freq

--------------------------------

WD_CTR

COUNT[15:0]

WD_SR.1

WDOVF

WD_OMR.0

RSTEN

Internal

Reset

= 0

PWL[15:0]

WD_SR.0

WDPEND

RSTALW

Write Access to WD_CR

RSTKEY = 0xC071

WD_OMR.1

WDEN

WD_MR

WDPDIV[2:0]

Programmable

Divider

(WDPDIV)

Count

Load

16-bit

Down-counter

ENA

LFCLK

(PCV[15:0])

WDCLK

Table 32. Watch Dog Example

WD Counter

Start Value

WDPDIV[2:0]

WDCLK

Time to WD

Pending

Time to WD

Overflow

0x07FF

000

LFCLK/2

0.109 s

0.125 s

0x0FFF

001

LFCLK/4

0.468 s

0.500 s

0x17FF

010

LFCLK/8

1.437 s

1.500 s

0xAFFF

101

LFCLK/128

175 s

176 s

0xFFFF

111

LFCLK/1024

1040 s

2048 s

AT91SAM7A2-AI Datasheet(PDF) 64 Page - ATMEL Corporation

AT91SAM7A2-AI Datasheet(HTML) 64 Page - ATMEL Corporation

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 ...More

Datasheet Download

Link URL