9/19

M48T35AY, M48T35AV

Table 10. Write Mode AC Characteristics

2. If E goes low simultaneously with W going low, the outputs remain in the high impedance state.

Symbol

Parameter

M48T35AY

M48T35AV

Unit

-70

-100

Min

Max

Min

Max

Write Cycle Time

70

100

ns

Address Valid to Write Enable Low

0

0

ns

Address Valid to Chip Enable Low

0

0

ns

Write Enable Pulse Width

50

80

ns

Chip Enable Low to Chip Enable High

55

80

ns

Write Enable High to Address Transition

0

10

ns

Chip Enable High to Address Transition

0

10

ns

Input Valid to Write Enable High

30

50

ns

Input Valid to Chip Enable High

30

50

ns

Write Enable High to Input Transition

5

5

ns

Chip Enable High to Input Transition

5

5

ns

(1, 2)

Write Enable Low to Output Hi-Z

25

50

ns

Address Valid to Write Enable High

60

80

ns

Address Valid to Chip Enable High

60

80

ns

(1, 2)

Write Enable High to Output Transition

5

10

ns

Setting the Clock

Bit D7 of the Control Register 7FF8h 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 (see

Table 11). Resetting the WRITE bit to a '0' then

transfers the values of all time registers 7FF9h-

7FFFh to the actual TIMEKEEPER counters and

allows normal operation to resume. The FT bit and

the bits marked as '0' in Table 11 must be written

to '0' to allow for normal TIMEKEEPER and RAM

operation. After the WRITE bit is reset, the next

clock update will occur within one second.

See the Application Note AN923 "TIMEKEEPER

rolling into the 21st century" on the for information

on Century Rollover.

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 the MSB of the seconds register. Setting it to

a '1' stops the oscillator. The M48T35AY/35AV is

shipped from STMicroelectronics with the STOP

bit set to a '1'. When reset to a '0', the M48T35AY/

35AV oscillator starts within 1 second.