m48t512y STMicroelectronics, m48t512y Datasheet - Page 11

• Manufacturer Part Number: m48t512y
• Description: 5.0 Or 3.3v, 4 Mbit 512 Kbit X 8 Timekeeper Sram
• Manufacturer: STMicroelectronics

CLOCK OPERATIONS
Reading the Clock
Updates to the TIMEKEEPER
be halted before clock data is read to prevent
reading data in transition (see
PORT™ TIMEKEEPER cells in the RAM array are
only data registers and not the actual clock
counters, so updating the registers can be halted
without disturbing the clock itself.
Updating is halted when a '1' is written to the
READ Bit, D6 in the Control Register (7FFF8h). As
long as a '1' remains in that position, updating is
halted. After a halt is issued, the registers reflect
the count; that is, the day, date, and time that were
current at the moment the halt command was is-
sued. All of the TIMEKEEPER registers are updat-
ed simultaneously. A halt will not interrupt an
update in progress. Updating occurs 1 second af-
ter the READ Bit is reset to a '0.'
Setting the Clock
Bit D7 of the Control Register (7FFF8h) is the
WRITE Bit. Setting the WRITE Bit to a '1,' like the
READ Bit, halts updates to the TIMEKEEPER reg-
isters. The user can then load them with the cor-
rect day, date, and time data in 24 hour BCD
format (see
Table 5. Register Map
Keys: S = SIGN Bit
Address
7FFFDh
7FFFCh
7FFFFh
7FFFEh
7FFFBh
7FFFAh
7FFF9h
7FFF8h
R = READ Bit
W = WRITE Bit
ST = STOP Bit
0 = Must be set to '0'
D7
ST
W
0
0
0
0
0
Table 5., page
D6
R
0
0
0
0
10 Years
10 Seconds
10 Minutes
D5
S
0
0
11). Resetting the
10 Hours
10 Date
®
Table
registers should
10 M
D4
0
5.). The Bi-
Data
D3
0
Calibration
D2
Seconds
WRITE Bit to a '0' then transfers the values of all
time registers 7FFFFh-7FFF9h to the actual TIME-
KEEPER counters and allows normal operation to
resume. After the WRITE Bit is reset, the next
clock update will occur approximately one second
later. See Application Note, AN923, “TIMEKEEP-
ER
Site for more information on Century Rollover.
Note: Upon power-up, both the WRITE Bit and the
READ Bit will be reset to '0.'
Stopping and Starting the Oscillator.
The oscillator may be stopped at any time. If the
device is going to spend a significant amount of
time on the shelf, the oscillator can be turned off to
minimize current drain on the battery. The STOP
bit is located at Bit D7 within 7FFF9h. Setting it to
a '1' stops the oscillator. The M48T512Y/V is
shipped from STMicroelectronics with the STOP
bit set to a '1.' When reset to a '0,' the M48T512Y/
V oscillator starts after approximately one second.
Note: It is not necessary to set the WRITE Bit
when setting or resetting the FREQUENCY TEST
Bit (FT) or the STOP Bit (ST).
Minutes
Month
Hours
Date
Year
®
Rolling Into the 21
Day
D1
D0
M48T512Y, M48T512V*
Seconds
st
Minutes
Control
Month
Hours
Date
Year
Day
Century” on the ST Web
Function/Range
BCD Format
00-99
01-12
01-31
01-07
00-23
00-59
00-59
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