M48T212Y datasheet(11/32 Pages) STMICROELECTRONICS

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M48T212Y, M48T212V

WRITE Mode

The M48T212Y/V is in the WRITE Mode whenever

W (WRITE Enable) and E (Chip Enable) are in a

low state after the address inputs are stable. The

start of a WRITE is referenced from the latter oc-

curring falling edge of W or E. A WRITE is termi-

nated by the earlier rising edge of W or E. The

addresses must be held valid throughout the cy-

cle. E or W must return high for a minimum of tE-

HAX from Chip Enable or tWHAX from WRITE

Enable prior to the initiation of another READ or

WRITE cycle. Data-in must be valid tDVWH prior to

the end of WRITE and remain valid for tWHDX af-

terward.

G should be kept high during WRITE cycles to

avoid bus contention; although, if the output bus

has been activated by a low on E and G a low on

W will disable the outputs tWLQZ after W falls.

When E is low during the WRITE, one of the on-

board TIMEKEEPER® registers will be selected

and data will be written into the device. When EX

is low (and E is high) an external SRAM location is

selected.

Note: Care should be taken to avoid taking both E

and EX low simultaneously to avoid bus conten-

tion.

Figure 7. WRITE Cycle Timing: RTC Control Signal Waveforms

Note: EX is assumed High.

AI02641

DQ0-DQ7

DATA IN

VALID

ADDRESS

tAVAV

tAVEH

tAVAV

WRITE

READ

DATA OUT

VALID

DATA OUT

VALID

tAVWH

tAVQV

tWLWH

tWHDX

tWHAX

tWHQX

tWLQZ

tDVWH

tGLQV

tEHQZ

tDVEH

DATA IN

VALID

tELEH

tEHAX

tAVEL

tEHDX

tAVWL

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