M48T86PC datasheet(11/23 Pages) STMICROELECTRONICS

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M48T86

Figure 10. Motorola Bus Read/Write Mode AC Waveforms

AI01649

tASD

tASW

AD0-AD7

(Write)

tCYC

tDSH

tDAS

tCS

tRWH

tAS

tDHW

R/W

tDSL

tRWS

tCH

AD0-AD7

(Read)

tDW

tAH

tAS

tOD

tDHR

PERIODIC INTERRUPT

The periodic interrupt will cause the IRQ pin to go

to an active state from once every 500ms to once

every 122µs. This function is separate from the

alarm interrupt which can be output from once per

second to once per day. The periodic interrupt rate

is selected using the same Register A bits which

select the square wave frequency (see Table 10).

Changing the Register A bits affects both the

square wave frequency and the periodic interrupt

output. However, each function has a separate en-

able bit in Register B. The periodic interrupt is en-

abled by the PIE bit (Register B; Bit 6). The

periodic interrupt can be used with software

counters to measure inputs, create output inter-

vals, or await the next needed software function.

ALARM INTERRUPT

The alarm interrupt provides the system processor

with an interrupt when a match is made between

the RTC's hours, minutes, and seconds bytes and

the corresponding alarm bytes.

The three alarm bytes can be used in two ways.

First, when the alarm time is written in the appro-

priate hours, minutes, and seconds alarm loca-

tions, the alarm interrupt is initiated at the specified

time each day if the Alarm Interrupt Enable bit

(Register B; Bit 5) is high. The second use is to in-

sert a "don't care" state in one or more of the three

alarm bytes. The "don't care" code is any hexadec-

imal value from C0 to FF. The two most significant

bits of each byte set the "don't care" condition

when at logic "1". An alarm will be generated each

hour when the "don't care" is are set in the hours

byte. Similarly, an alarm is generated every minute

with "don't care" codes in the hour and minute

alarm bytes. The "don't care" codes in all three

alarm bytes create an interrupt every second.

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