Rainbow Electronics DS1673 - Manual (Page 2)

DS1673
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Automatic backup and write protection of external SRAM is provided through the V
CCO
, CEOL , and
CEOH pins. The backup energy source used to power the RTC is also used to retain RAM data in the
absence of V
CC
through the V
CCO
pin. The chip enable outputs to RAM ( CEOL and CEOH ) are controlled
during power transients to prevent data corruption.
The microprocessor monitor circuitry of the DS1673 provides three basic functions. First, a precision
temperature-compensated reference and comparator circuit monitors the status of V
CC
. When an out-of-
tolerance condition occurs, an internal power-fail signal is generated which forces the reset to the active
state. When V
CC
returns to an in-tolerance condition, the reset signals are kept in the active state for
250 ms to allow the power supply and processor to stabilize. The second microprocessor monitor
function is pushbutton reset control. The DS1673 debounces a pushbutton input and guarantees an active
reset pulse width of 250 ms. The third function is a watchdog timer. The DS1673 has an internal timer
that forces the reset signals to the active state if the strobe input is not driven low prior to watchdog
time-out.
The DS1673 also provides a 3-channel, 8-bit successive approximation analog-to-digital converter. The
converter has an internal 2.55 volt (typical) reference voltage generated by an on-board band-gap circuit.
The A/D converter is monotonic (no missing codes) and has an internal analog filter to reduce high
frequency noise.
OPERATION
The block diagram in Figure 1 shows the main elements of the DS1673. The following paragraphs
describe the function of each pin.
DS1673 BLOCK DIAGRAM Figure 1