DS1558

2 of 18

PIN DESCRIPTION

PIN

NAME

FUNCTION

1, 13, 39

41, 43

N.C.

No Connection

2

A18

3

A16

4

A14

5

A12

6

A7

7

A6

8

A5

9

A4

10

A3

11

A2

12

A1

14

A0

27

A10

29

A11

30

A9

31

A8

32

A13

36

A15

44

A17

Address Inputs for Address Decode. The DS1558 uses the address inputs to determine

whether or not a read or write cycle should be directed to the attached SRAM or to the

RTC registers.

15

DQ0

16

DQ1

17

DQ2

19

DQ3

20

DQ4

21

DQ5

22

DQ6

23

DQ7

Data Input/Outputs. Data input/output pins for the RTC registers.

18, 45,

48

GND

Ground

24

CER

Active-Low Chip-Enable RAM.

CE is passed through to CER, with an added

propagation delay. When the signals on A0–A18 match an RTC address,

CER is held

high, disabling the SRAM. If

OE is also low, the RTC outputs data on DQ0–DQ7.

25

OER

Active-Low Output-Enable RAM.

OE is passed through to OER, with an added

propagation delay. When the signals on A0–A18 match an RTC address,

CER is held

high, disabling the SRAM. If

CE is also low, the RTC outputs data on DQ0–DQ7.

26

CE

Active-Low Chip-Enable Input. Used to access the RTC and the external SRAM.

28

OE

Active-Low Output-Enable Input. Used to access the RTC and the external SRAM.

33

IRQ/FT

Active-Low Interrupt/Frequency-Test Output. This pin is used to output the alarm

interrupt or the frequency test signal. It is open drain and requires an external pullup

resistor.

34

WE

Active-Low Write Enable. Used to write data to the RTC registers.