TABLE IIa Interrupt Selection Data

Mode Address 15 Write Mode

Function

DB3

DB2

DB1

DB0

No Interrupt

X

0

0

0

Int at 60 Sec Intervals

01

1

0

0

Int at 50 Sec Intervals

01

0

1

0

Int at 05 Sec Intervals

01

0

0

1

a

166 ms

TABLE IIb Interrupt Read Back (Status)

Mode Address 15 Read Mode

Interrupt Status

DB3

DB2

DB1

DB0

Reset

X

0

0

0

60 Sec Signal

X

1

0

0

50 Sec Signal

X

0

1

0

05 Sec Signal

X

0

0

1

TABLE III Years Status Register

Mode Address 13 Write Mode

DB3

DB2

DB1

DB0

Leap Year

1

0

0

0

Leap Year-1

0

1

0

0

Leap Year-2

0

0

1

0

Leap Year-3

0

0

0

1

Note

Leap year counter rolls over on December 31

235959

INTERRUPT SYSTEM

The interrupt output and its frequency of operation is en-

abled by writing to address 15 (see Table IIa) To ensure

correct operation the interrupt should be serviced within

166 ms

The interrupt is initialized by writing ‘‘0’’ to address 15 and

reading the interrupt ie reading at address 15 three times

Initialization must be performed at power on and also if the

interrupt is not serviced correctly within 166 ms

SERVICING THE INTERRUPT

In a typical system the open drain interrupt output is wired to

the processor interrupt system Hence when the interrupt

timer times out the interrupt output is pulled low and the

processor is interrupted

The processor may then reset the interrupt by utilizing the

following procedure

Read Address 15 three times

This resets the interrupt output and restarts the interrupt

timer when in the repeat mode

It is recommended that the interrupt output is connected to

a unique processor port

CRYSTAL PARAMETERS

Figure 4 is an electrical representation of the crystal along

with some typical values The 32768 kHz crystal is an NT

CUT (tuning fork type) or XY BAR for use in a parallel reso-

nant Pierce oscillator

TLF6681 – 5

0003 pF

35 kX

30 pF

FIGURE 4 Typical Crystal Parameters

DEVICE INITIALIZATION AND OSCILLATOR SETTING

When first installed or if the battery back-up has failed the

MM58174A will require to be properly initialized The follow-

ing sequence is a suggested flow of operations to achieve

this

Action

Result

1) Apply power

Clears interrupt timer

chain

2) Write ‘‘0’’ to address 15

3) Read 3 times from

Clears interrupt output

address 15

logic

4) Write ‘‘0’’ on DB3 to

Clears test mode

address 0

5) Write ‘‘0’’ on DB0 to

Stops clock running

address 14

6) Set up timekeeping

Load real-time into device

registers

time registers minutes to

leap years

7) Write ‘‘1’’ on DB0 to

Starts timekeeping

address 14

synchronized to an

external time source

8) Program and start

Commence interrupt

interrupts

timing if so required

OSCILLATOR SETTING

Directly connecting a frequency meter to the Crystal Out pin

(14) will not allow correct frequency setting because of the

extra capacitive loading of the meter One possibility for set-

ting is to use a high impedance probe or a CMOS buffer to

keep the loading as low as possible (eg 100x2pF probe)

Alternatively a buffered output of 16384 kHz OSC2 can

be produced on DB0 by applying the following procedure

Action

Result

1) Write a ‘‘1’’ on DB3 to

Selects test mode

address 0

2) Write a ‘‘1’’ on DB0 to

Starts clock timing

address 14

3) Read at address 1 (tenths

‘‘Data Changed’’ signal is

of secs)

read

4) Read at address 1 and

16384 kHz appears on

HOLD the strobe LOW

DB0

5) Adjust trimmer capacitor

There must be no extra activity on the RD line between

steps 3 and 4 or only the normal ‘‘Data Changed’’ signal will

be observed on the data bus Thus if the normal host proc-

essor system is being used to generate the chip waveforms

proper care must be taken

5