Address Map

The bq4845 provides 16 bytes of clock and control status

registers. Table 1 is a map of the bq4845 registers, and

Table 2 describes the register bits.

Clock Memory Interface

The bq4845 has the same interface for clock/calendar

and control information as standard SRAM. To read and

write to these locations, the user must put the bq4845 in

the proper mode and meet the timing requirements.

Read Mode

The bq4845 is in read mode whenever OE (Output en-

able) is low and CS (chip select) is low. The unique ad-

dress, specified by the 4 address inputs, defines which

one of the 16 clock/calendar bytes is to be accessed. The

bq4845 makes valid data available at the data I/O pins

last address input signal is stable, and providing the CS

and OE (output enable) access times are met. If the CS

and OE access times are not met, valid data is available

CS and OE control the state of the eight three-state

4

Ad-

dress

(h)

D7

D6

D5

D4

D3

D2

D1

D0

12-Hour

Range (h)

Register

0

0

10-second digit

1-second digit

00–59

Seconds

1

ALM1

ALM0

1-second digit

00–59

Seconds alarm

10-second digit

2

0

10-minute digit

1-minute digit

00–59

Minutes

3

ALM1

ALM0

1-minute digit

00–59

Minutes alarm

10-minute digit

4

PM/AM

0

10-hour digit

1-hour digit

01–12 AM/ 81– 92 PM Hours

5

ALM1

ALM0

10-hour digit

1-hour digit

01–12 AM/ 81–92 PM Hours alarm

PM/AM

6

0

0

10-day digit

1-day digit

01–31

Day

7

ALM1

ALM0

10-day digit

1-day digit

01–31

Day alarm

8

0

0

0

Day-of-week digit

01–07

Day-of-week

9

0

0

0

10 mo.

1-month digit

01–12

Month

A

10-year digit

1-year digit

00–99

Year

B

*

WD2

WD1

WD0

RS3

RS2

RS1

RS0

Programmable

rates

C

*

*

AIE

PIE

PWRIE ABE

Interrupt en-

ables

D

*

*

AF

PF

PWRF BVF

Flags

E

*

*

UTI

STOP

24/12

DSE

Control

F

*

*

*

*

*

*

*

*

Unused

Notes:

* = Unused bits; unwritable and read as 0.

0 = should be set to 0 for valid time/calendar range.

Clock calendar data in BCD. Automatic leap year adjustment.

PM/AM = 1 for PM; PM/AM = 0 for AM.

DSE = 1 enables daylight savings adjustment.

24/12 = 1 enables 24-hour data representation; 24/12 = 0 enables 12-hour data representation.

Day-of-Week coded as Sunday = 1 through Saturday = 7.

BVF = 1 for valid battery.

STOP = 1 turns the RTC on; STOP = 0 stops the RTC in back-up mode.

Table 1. bq4845 Clock and Control Register Map

Aug. 1995

bq4845/bq4845Y