M48T08-150PC1TR STMICROELECTRONICS [STMicroelectronics], M48T08-150PC1TR Datasheet - Page 13

• Manufacturer Part Number: M48T08-150PC1TR
• Description: CMOS 8K x 8 TIMEKEEPER SRAM
• Manufacturer: STMICROELECTRONICS [STMicroelectronics]

CLOCK OPERATIONS
Reading the Clock
Updates to the TIMEKEEPER
be halted before clock data is read to prevent
reading data in transition. The BiPORT™ TIME-
KEEPER cells in the RAM array are only data reg-
isters and not the actual clock counters, so
updating the registers can be halted without dis-
turbing the clock itself.
Updating is halted when a '1' is written to the
READ Bit, the seventh bit in the control register.
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 the time that
were current at the moment the halt command was
issued.
All of the TIMEKEEPER registers are updated si-
multaneously. A halt will not interrupt an update in
progress. Updating is within a second after the bit
is reset to a '0.'
Table 5. Register Map
Keys: S = SIGN Bit
Address
1FFDh
1FFCh
1FFFh
1FFEh
1FFBh
1FFAh
1FF9h
1FF8h
FT = FREQUENCY TEST Bit (Set to '0' for normal clock operation)
R = READ Bit
W = WRITE Bit
ST = STOP Bit
0 = Must be set to '0'
D7
ST
W
0
0
0
0
0
D6
FT
R
0
0
0
10 Years
10 Seconds
10 Minutes
D5
S
0
0
10 Hours
10 Date
®
registers should
10 M
D4
0
Data
D3
0
Calibration
D2
Seconds
Setting the Clock
The eighth bit of the control register is the WRITE
Bit. Setting the WRITE Bit to a '1,' like the READ
Bit, halts updates to the TIMEKEEPER registers.
The user can then load them with the correct day,
date, and time data in 24 hour BCD format (on
ble
fers the values of all time registers (1FF9h-1FFFh)
to the actual TIMEKEEPER counters and allows
normal operation to resume. The FT Bit and the
bits marked as '0' in
to allow for normal TIMEKEEPER and RAM oper-
ation.
See the Application Note AN923, “TIMEKEEPER
Rolling Into the 21
Century Rollover.
Minutes
Month
Hours
Date
Year
5.). Resetting the WRITE Bit to a '0' then trans-
Day
D1
D0
M48T08, M48T08Y, M48T18
st
Table 5.
Century” for information on
Seconds
Minutes
Control
Month
Hours
Date
Year
Day
Function/Range
BCD Format
must be written to '0'
00-99
01-12
01-31
01-07
00-23
00-59
00-59
13/27
Ta-
®