DS1670

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The third microprocessor monitoring function provided by the DS1670 is a watchdog timer. The

predetermined time period. The time period is set by the Time Delay (TD) bits in the Watchdog Register.

The time delay can be set to 250ms, 500ms, or 1000ms (see Figure 5). If TD0 and TD1 are both set to 0,

the watchdog timer is disabled. When enabled, the watchdog timer starts timing out from the set time

address signals, data signals, and/or control signals. To guarantee that the watchdog timer does not

timeout, a high-to-low transition must occur at or less than the minimum period.

WATCHDOG TIMEOUT CONTROL Figure 5

WATCHDOG REGISTER

BIT 7

BIT 6

BIT 5

BIT 4

BIT 3

BIT 2

BIT 1

BIT 0

0

0

0

0

0

0

TD1

TD0

WATCHDOG TIMEOUT

TD1

TD0

WATCHDOG TIMEOUT

0

0

Watchdog disabled

0

1

250ms

1

0

500ms

1

1

1000ms

ANALOG-TO-DIGITAL CONVERTER

The DS1670 provides a 3-channel, 8-bit analog-to-digital converter. The ADC reference voltage (2.55V

typical) is derived from an on-chip band-gap circuit. Three multiplexed analog inputs are provided

through the AIN0, AIN1, and AIN2 pins. The ADC is monotonic (no missing codes) and uses a

successive approximation technique to convert the analog signal into a digital code. An A/D conversion is

the process of assigning a digital code to an analog input voltage. This code represents the input value as

a fraction of the full-scale voltage (FSV) range. Thus, the FSV range is then divided by the ADC into 256

codes (8 bits). The FSV range is bounded by an upper limit equal to the reference voltage and the lower

limit, which is ground. The DS1670 has a FSV of 2.55V (typical) that provides a resolution of 10mV. An

input voltage equal to the reference voltage converts to FFh while an input voltage equal to ground

converts to 00h. The relative linearity of the ADC is ±0.5 LSB.

The ADC selects from one of three different analog inputs (AIN0–AIN2). The input that is selected is

determined by the Analog Input Select (AIS) bits in the Control Register. Table 2 lists the specific analog