Rainbow Electronics DDS1693 - Manual (Page 3)

DS1689/DS1693
3 of 32
V
CCO
(External SRAM Power Supply Output) - This pin will be internally connected to V
CCI
when
V
CCI
is within nominal limits. However, during power fail, V
CCO
will be internally connected to the V
BAT
or V
BAUX
(whichever is larger). For 5-volt operation, switch over from V
CCI
to the backup supply occurs
when V
CCI
drops below the larger of V
BAT
and V
BAUX
. For 3-volt operation, switch over from V
CCI
to the
backup supply occurs at V
PF
if V
PF
is less than V
BAT
and V
BAUX
. If V
PF
is greater than V
BAT
and V
BAUX
,
the switch from V
CCI
to the backup supply occurs when V
CCI
drops below the larger of V
BAT
and V
BAUX
.
DS1689/DS1693 BLOCK DIAGRAM Figure 1
SQW (Square Wave Output) - The SQW pin can output a signal from one of 13 taps provided by the 15
internal divider stages of the real time clock. The frequency of the SQW pin can be changed by
programming Register A as shown in Table 2. The SQW signal can be turned on and off using the SQWE
bit in Register B. A 32 kHz SQW signal is output when SQWE=1, the Enable 32 kHz (E32K) bit in
extended register 04BH is a logic 1, and V
CC
is above V
PF
. A 32 kHz square wave is also available when
V
CC
is less than V
PF
if E32K=1, ABE=1, and voltage is applied to V
BAUX
.