DS1642 Maxim, DS1642 Datasheet - Page 4

• Manufacturer Part Number: DS1642
• Description: The DS1642 is a 2k x 8 nonvolatile static RAM and a full-function real-time clock (RTC), both of which are accessible in a bytewide format
• Manufacturer: Maxim

SETTING THE CLOCK
The 8th bit of the control register is the write bit. Setting the write bit to a 1, like the read bit, halts
updates to the DS1642 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
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 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.,
CLOCK ACCURACY
The DS1642 is guaranteed to keep time accuracy to within 1 minute per month at 25C. Dallas
Semiconductor calibrates the clock at the factory by using special calibration nonvolatile-tuning elements.
The DS1642 does not require additional calibration and temperature deviations will have a negligible
effect in most applications. For this reason, methods of field clock calibration are not available and not
necessary.
Table 2. REGISTER MAP–BANK1
Note: All indicated “X” bits are not used but must be set to “0” during write cycle to ensure proper clock
operation.
OSC = STOP BIT
W = WRITE BIT
ADDRESS
7FD
7FA
7FE
7FC
7FB
CE
7FF
7F9
7F8
low, and
OSC
B7
—
W
X
X
X
X
X
R = READ BIT
X = UNUSED
OE
low) and address for seconds register remain valid and stable.
B6
FT
—
—
—
X
X
X
R
FT = FREQUENCY TEST
B5
—
—
—
—
—
X
X
X
B4
—
—
—
—
—
—
X
X
DATA
OSC
B3
—
—
—
—
—
—
X
X
4 of 13
bit is the MSB for the seconds registers. Setting it to
B2
—
—
—
—
—
—
—
X
B1
—
—
—
—
—
—
—
X
B0
—
—
—
—
—
—
—
X
Minutes
Seconds
Control
Month
Hour
Year
Date
Day
FUNCTION
00–99
01–12
01–31
00–23
00–59
00–59
00–59
A
DS1642