M41T00M STMICROELECTRONICS [STMicroelectronics], M41T00M Datasheet - Page 8

• Manufacturer Part Number: M41T00M
• Description: Serial Access TIMEKEEPER
• Manufacturer: STMICROELECTRONICS [STMicroelectronics]

M41T00
Figure 6. Serial Bus Data Transfer Sequence
Figure 7. Acknowledgment Sequence
CLOCK OPERATION
The eight byte clock register (see Table 3) is used
to both set the clock and to read the date and time
from the clock, in a binary coded decimal format.
Seconds, Minutes, and Hours are contained within
the first three registers. Bits D6 and D7 of clock
register 2 (Hours Register) contain the CENTURY
ENABLE Bit (CEB) and the CENTURY Bit (CB).
Setting CEB to a ’1’ will cause CB to toggle, either
from ’0’ to ’1’ or from ’1’ to ’0’ at the turn of the cen-
tury (depending upon its initial state). If CEB is set
to a ’0’, CB will not toggle. Bits D0 through D2 of
register 3 contain the Day (day of week). Registers
4, 5 and 6 contain the Date (day of month), Month
and Years. The final register is the Control Regis-
ter (this is described in the Clock Calibration sec-
tion). Bit D7 of register 0 contains the STOP Bit
(ST). Setting this bit to a ’1’ will cause the oscillator
8/15
SCLK FROM
MASTER
DATA OUTPUT
BY TRANSMITTER
DATA OUTPUT
BY RECEIVER
CLOCK
DATA
CONDITION
START
START
MSB
1
DATA VALID
DATA LINE
STABLE
DATA ALLOWED
CHANGE OF
2
to stop. If the device is expected to spend a signif-
icant amount of time on the shelf, the oscillator
may be stopped to reduce current drain. When re-
set to a ’0’ the oscillator restarts within one second.
The seven Clock Registers may be read one byte
at a time, or in a sequential block. The Control
Register (Address location 7) may be accessed in-
dependently. Provision has been made to assure
that a clock update does not occur while any of the
seven clock addresses are being read. If a clock
address is being read, an update of the clock reg-
isters will be delayed by 250ms to allow the read
to be completed before the update occurs. This
will prevent a transition of data during the read.
Note: This 250ms delay affects only the clock reg-
ister update and does not alter the actual clock
time.
LSB
8
ACKNOWLEDGEMENT
CLOCK PULSE FOR
CONDITION
STOP
9
AI00587
AI00601