DS1643-120 DALLAS [Dallas Semiconductor], DS1643-120 Datasheet - Page 3

• Manufacturer Part Number: DS1643-120
• Description: Nonvolatile Timekeeping RAM
• Manufacturer: DALLAS [Dallas Semiconductor]

DS1643 TRUTH TABLE Table 1
SETTING THE CLOCK
The 8–bit of the control register is the write bit. Setting
the write bit to a one, like the read bit, halts updates to
the DS1643 registers. The user can then load them with
the correct day, date and time data in 24 hour BCD for-
mat. Resetting the write bit to a zero 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 in-
crease the shelf life, the oscillator can be turned off to
minimize current drain from the battery. The OSC bit is
the MSB for the seconds 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
5 VOLTS
5 VOLTS
5 VOLTS
<4.5 VOLTS
>V
<V
V
CC
BAT
BAT
10%
10%
10%
V
CE
V
V
V
X
X
X
IH
IL
IL
IL
CE2
V
V
V
V
X
X
X
IH
IH
IH
IL
OE
V
V
X
X
X
X
X
IH
IL
WE
V
V
V
X
X
X
X
IH
IH
IL
DESELECT
DESELECT
DESELECT
DESELECT
WRITE
MODE
READ
READ
running, the LSB of the seconds 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,
CE2 high, and address for seconds register remain valid
and stable).
CLOCK ACCURACY
The DS1643 is guaranteed to keep time accuracy to
within 1 minute per month at 25 C. The clock is cali-
brated at the factory by Dallas Semiconductor using
special calibration nonvolatile tuning elements. The
DS1643 does not require additional calibration and tem-
perature deviations will have a negligible effect in most
applications. For this reason, methods of field clock cal-
ibration are not available and not necessary. Attempts
to calibrate the clock that may be used with similar de-
vice types (MK48T08 family) will not have any effect
even though the DS1643 appears to accept calibration
data.
DATA OUT
DATA IN
HIGH Z
HIGH Z
HIGH Z
HIGH Z
HIGH Z
DQ
DATA RETENTION
CMOS STANDBY
STANDBY
STANDBY
POWER
ACTIVE
ACTIVE
ACTIVE
MODE
041697 3/11
DS1643