M48TMH1 STMICROELECTRONICS [STMicroelectronics], M48TMH1 Datasheet - Page 17

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

REGISTER C
MSB
IRQF. Interrupt Request Flag
The Interrupt Request Flag (IRQF) bit is set to a
one when one or more of the following are true:
PF = PIE = 1
AF = AIE = 1
UF = UIE = 1
(i.e. IRQF = PF*PIE+AF*AIE+UF*UIE)
PF. Periodic Interrupt Flag
The Periodic Interrupt Flag (PF) is a read-only bit
which is set to a one when an edge is detected on
the selected tap of the divider chain. The RS3-RS0
bits establish the periodic rate. PF is set to a one
independent of the state of the PIE bit. The IRQ
signal is active and will set the IRQF bit. The PF bit
is cleared by a RST or a software read of Register
C.
REGISTER D
MSB
VRT. Valid Ram And Time
The Valid RAM and Time (VRT) bit is set to the
one state by STMicroelectronics prior to shipment.
This bit is not writable and should always be a one
when read. If a zero is ever present, an exhausted
internal lithium cell is indicated and both the con-
tents of the RTC data and RAM data are question-
able. This bit is unaffected by RST.
IRQF
BIT7
BIT7
VRT
BIT6
BIT6
PF
0
BIT5
BIT5
AF
0
BIT4
BIT4
UF
0
AF. Alarm Flag
A one in the AF (Alarm Interrupt Flag) bit indicates
that the current time has matched the alarm time.
If the AIE bit is also a one, the IRQ pin will go low
and a one will appear in the IRQF bit. A RST or a
read of Register C will clear AF.
UF. Update Ended Interrupt Flag
The Update Ended Interrupt Flag (UF) bit is set af-
ter each update cycle. When the UIE bit is set to a
one, the one in the UF bit causes the IRQF bit to
be a one. This will assert the IRQ pin. UF is
cleared by reading Register C or an RST.
BIT 0 through 3. Unused Bits
Bit 3-Bit 0 are unused. These bits always read
zero and cannot be written.
BIT 0 through 6. Unused Bits
The remaining bits of Register D are not usable.
They cannot be written and when read, they will al-
ways read zero.
BIT3
BIT3
0
0
BIT2
BIT2
0
0
BIT1
BIT1
0
0
M48T86
BIT0
BIT0
0
0
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