ISL12020MIRZ-T7A Datasheet, PDF(23/34 Page) Intersil Corporation – Low Power RTC with Battery Backed SRAM, Integrated ±5ppm Temperature Compensation and Auto Daylight Saving

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ISL12020MIRZ-T7A Datasheet, PDF (23/34 Pages) Intersil Corporation – Low Power RTC with Battery Backed SRAM, Integrated ±5ppm Temperature Compensation and Auto Daylight Saving

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ISL12020M

ALARM

SCA0

MNA0

HRA0

DTA0

MOA0

DWA0

BIT

7 6 5 4 3 2 1 0 HEX DESCRIPTION

0 0 0 0 0 0 0 0 00h Seconds disabled

1 0 1 1 0 0 0 0 B0h Minutes set to 30,

enabled

1 0 0 1 0 0 0 1 91h Hours set to 11,

enabled

1 0 0 0 0 0 0 1 81h Date set to 1,

enabled

1 0 0 0 0 0 0 1 81h Month set to 1,

enabled

0 0 0 0 0 0 0 0 00h Day of week

disabled

After these registers are set, an alarm will be generated when the

RTC advances to exactly 11:30 a.m. on January 1 (after seconds

changes from 59 to 00) by setting the ALM bit in the status register

to â1â and also bringing the IRQ/FOUT output low.

Example 2

â¢ Pulsed interrupt once per minute (IM = â1â)

â¢ Interrupts at one minute intervals when the seconds register is

at 30s.

â¢ Set Alarm registers as follows:

TABLE 21.

BIT

ALARM

DESCRIPTION

SCA0

1 0 1 1 0 0 0 0 B0h Seconds set to 30,

enabled

MNA0 0 0 0 0 0 0 0 0 00h Minutes disabled

HRA0 0 0 0 0 0 0 0 0 00h Hours disabled

DTA0 0 0 0 0 0 0 0 0 00h Date disabled

MOA0 0 0 0 0 0 0 0 0 00h Month disabled

DWA0 0 0 0 0 0 0 0 0 00h Day of week disabled

Once the registers are set, the following waveform will be seen at

IRQ/FOUT:

RTC AND ALARM REGISTERS ARE BOTH â30sâ

60s

FIGURE 15. IRQ/FOUT WAVEFORM

Note that the status register ALM bit will be set each time the

alarm is triggered, but does not need to be read or cleared.

Time Stamp VDD to Battery Registers (TSV2B)

The TSV2B Register bytes are identical to the RTC register bytes,

except they do not extend beyond the Month. The Time Stamp

captures the FIRST VDD to Battery Voltage transition time, and will

not update upon subsequent events, until cleared (only the first

event is captured before clearing). Set CLRTS = 1 to clear this

Note that the time stamp registers are cleared to all â0â,

including the month and day, which is different from the RTC and

alarm registers (those registers default to 01h). This is the

indicator that no time stamping has occurred since the last clear

or initial power-up. Once a time stamp occurs, there will be a non-

zero time stamp.

Time Stamp Battery to VDD Registers (TSB2V)

The Time Stamp Battery to VDD Register bytes are identical to

the RTC register bytes, except they do not extend beyond Month.

The Time Stamp captures the LAST transition of VBAT to VDD

(only the last event of a series of power-up/down events is

retained). Set CLRTS = 1 to clear this register (Add 09h,

PWR_VDD register).

DST Control Registers (DSTCR)

8 bytes of control registers have been assigned for the Daylight

Savings Time (DST) functions. DST beginning (set Forward) time

is controlled by the registers DstMoFd, DstDwFd, DstDtFd, and

DstHrFd. DST ending time (set Backward or Reverse) is controlled

by DstMoRv, DstDwRv, DstDtRv and DstHrRv.

Tables 22 and 23 describe the structure and functions of the DSTCR.

DST FORWARD REGISTERS (20H TO 23H)

DST forward is controlled by the following DST Registers:

DST Enable

DSTE is the DST Enabling Bit located in Bit 7 of register 20h

(DstMoFdxx). Set DSTE = 1 will enable the DSTE function. Upon

powering up for the first time (including battery), the DSTE bit

defaults to â0â. When DSTE is set to â1â the RTC time must be at

least one hour before the scheduled DST time change for the

correction to take place. When DSTE is set to â0â, the DSTADJ bit

in the Status Register automatically resets to â0â.

DST Month Forward

DstMoFd sets the Month that DST starts. The format is the same

as for the RTC register month, from 1 to 12. The default value for

the DST begin month is 00h.

DST Day/Week Forward

DstDwFd contains both the Day of the Week and the Week of the

Month data for DST Forward control. DST can be controlled either

by actual date or by setting both the Week of the month and the

Day of the Week. DstDwFdE sets the priority of the Day/Week

over the Date. For DstDwFdE = 1, Day/Week is the priority. You

must have the correct Day of Week entered in the RTC registers

for the Day/Week correction to work properly.

FN6667.5

December 13, 2011

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