Clock operation

M41T00CAP

14/27

Doc ID 14557 Rev 5

4

Clock operation

The 8-byte register map (see Table 2) 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 02h (century/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 century

(depending upon its initial state). If CEB is set to a '0,' CB will not toggle. Bits D0 through D2

of Register 03h contain the Day (day of week). Registers 04h, 05h, and 06h contain the date

(day of month), month and years. The eighth clock register is the calibration register (this is

described in the clock calibration section). Bit D7 of register 00h contains the STOP bit (ST).

Setting this bit to a '1' will cause the oscillator to stop. If the device is expected to spend a

significant amount of time on the shelf, the oscillator may be stopped to reduce current

drain. When reset 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 calibration register (address

location 07h) may be accessed independently. Provision has been made to ensure 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 registers will be halted. This will prevent

a transition of data during the READ.

Keys:

0 = must be set to '0'

CB = century bit

CEB = century enable bit

FT = frequency test bit

OF = oscillator fail bit

OUT = output level

S = sign bit

ST = stop bit

Addr

Function/range BCD format

D7

D6

D5

D4

D3

D2

D1

D0

00h

ST

10 seconds

Seconds

Seconds

00-59

01h

OF

10 minutes

Minutes

Minutes

00-59

02h

CEB

CB

10 hours

Hours (24-hour format)

Century/hours

0-1/00-23

03h

0000

0

Day of week

Day

01-7

04h

0

0

10 date

Date: day of month

Date

01-31

05h

0

0

0

10M

Month

Month

01-12

06h

10 years

Year

Year

00-99

07h

OUT

FT

S

Calibration

Calibration