M48TMH1 STMICROELECTRONICS [STMicroelectronics], M48TMH1 Datasheet - Page 11

• Manufacturer Part Number: M48TMH1
• Description: 5V PC REAL TIME CLOCK
• Manufacturer: STMICROELECTRONICS [STMicroelectronics]

Figure 10. Motorola Bus Read/Write Mode AC Waveforms
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.
AS
DS
R/W
E
AD0-AD7
(Write)
AD0-AD7
(Read)
tDAS
tASW
tDSL
tAS
tAS
tCS
tAH
tRWS
tCYC
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.
tAH
tASD
tOD
tDSH
tDW
tRWH
AI01649
tCH
tDHW
tDHR
M48T86
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