Setting the clock, Stopping and starting the clock oscillator, Frequency test bit – Rainbow Electronics DS1647P User Manual
Page 3
DS1647/DS1647P
3 of 11
BLOCK DIAGRAM DS1647 Figure 1
TRUTH TABLE DS1647 Table 1
V
CC
CE
OE
WE
MODE
DQ
POWER
V
IH
X
X
DESELECT
HIGH-Z
STANDBY
X
X
X
DESELECT
HIGH-Z
STANDBY
V
IL
X
V
IL
WRITE
DATA IN
ACTIVE
V
IL
V
IL
V
IH
READ
DATA OUT
ACTIVE
5V
± 10%
V
IL
V
IH
V
IH
READ
HIGH-Z
ACTIVE
<4.5V >V
BAT
X
X
X
DESELECT
HIGH-Z
CMOS STANDBY
<V
BAT
X
X
X
DESELECT
HIGH-Z
DATA RETENTION
MODE
SETTING THE CLOCK
The MSB Bit, B7, of the control register is the write bit. Setting the write bit to a 1, like the read bit halts
updates to the DS1647 registers. The user can then load them with the correct day, date and time data in
24-hour BCD format. Resetting the write bit to a 0 then transfers those values to the actual clock counters
and allows normal operation to resume.
STOPPING AND STARTING THE CLOCK OSCILLATOR
The clock oscillator may be stopped at any time. To increase the shelf life, the oscillator can be turned off
to minimize current drain from the battery. The
OSC
bit is the MSB for the second’s registers. Setting it
to a 1 stops the oscillator.
FREQUENCY TEST BIT
Bit 6 of the day byte is the frequency test bit. When the frequency test bit is set to logic 1 and the
oscillator is running, the LSB of the second’s register will toggle at 512 Hz. When the seconds register is
being read, the DQ0 line will toggle at the 512 Hz frequency as long as conditions for access remain valid
(i.e.,
CE
low,
OE
low, and address for seconds register remain valid and stable).