DS1680 datasheet(2/23 Pages) DALLAS

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DS1680

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Automatic backup and write protection of an external SRAM is provided through the VCCO and

CEO pins. The backup energy source used to power the RTC is also used to retain RAM data in the

absence of VCC through the VCCO pin. The chip-enable output to SRAM, CE0 , is controlled during power

transients to prevent data corruption.

The DS1680’s microprocessor- monitor circuitry provides three basic functions. First, a precision

temperature-compensated reference and comparator circuit monitors the status of VCC. When an out-of-

tolerance condition occurs, an internal power-fail signal is generated that forces

RST to the active state.

When VCC returns to an in- tolerance condition, the RST signal is kept in the active state for tRPU to allow

the power supply and processor to stabilize. The DS1680 debounces a pus hbutton input and guarantees an

active RST pulse width of tRST . The third function is a watchdog timer. The DS1680’s internal timer

forces the RST signal to the active state if the strobe input is not driven low prior to watchdog time-out.

The DS1680 also provides a touch-screen controller along with a 10-bit successive approximation ADC.

The ADC is monotonic (no missing codes) and has an internal analog filter to reduce high frequency

noise.

DS1680 BLOCK DIAGRAM Figure 1

CLOCK

OSC

CLOCK

GEN

PANEL

DRIVE

CONVERT

CONTROL

10-BIT

ADC

INPUT

MUX

TOUCH

DETECT

POWER

CONTROL

RTC

SERIAL

INTERFACE

WATCHDOG

OUTPUT

MUX

BHE

OUT_SELECT

PEN_SELECT

AIN0

AIN1

COEN

CONVERT

PEN_OFF

PD_RST

D0-D7

OSCIN

INT

SCLK

I/O

RST

POWER SWITCH,

WRITE PROTECT,

NV CONTROL,

AND

POWER FAIL

WARNING

VCC

VBAT

VCCO

CEI

CEO

PFI

PFO

ANSELIN

X+

X-

Y+

Y-

NEW_DATA

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