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70 CMX158886 cpuModule BDM-610000049 Rev G
0Bh 11 RTC Status Register B
• Bit 7: Inhibit Update - When high, the RTC is prevented from
updating.
• Bit 6: Periodic Interrupt Enable - When high, the RTC IRQ will
be asserted by the periodic interrupt.
• Bit 5: Alarm Interrupt Enable - When high, the RTC IRQ will be
asserted when the current time matches the alarm time.
• Bit 4: Update Ended Interrupt Enable - When high, the RTC IRQ
will be asserted every time the RTC updates (once per second).
• Bit 3: Square Wave Enable - Not used.
• Bit 2: Data Mode - Sets the data format of the RTC
clock/calendar registers (0=BCD, 1=binary). This is typically set
to BCD mode.
• Bit 1: Hours Byte Format - Sets the hour byte to 12 or 24 hour
time (0=12 hour, 1=24 hour). This is typically set to 24 hour
mode.
• Bit 0: Daylight Savings Enable - When high, the RTC will
automatically update itself for Daylight Savings Time. It is
recommended to leave this bit low and let the operating system
manage time zones and DST.
0Ch 12 RTC Status Register C (Read Only)
• Bit 7: IRQ Flag - Indicates that the Real Time Clock IRQ is
asserted. Goes high whenever one of the enabled interrupt
conditions in Register B occurs.
• Bit 6: Periodic Flag
• Bit 5: Alarm Flag
• Bit 4: Update Ended Flag
• Bit 3-0: Reserved
Reading this register will also clear any of set flag (IRQ, Periodic, Alarm, Update
Ended). Note that even if the interrupt source is not enabled in Register B, the
flags in Register C bits 4, 5, and 6 may still be set.
0Dh 13 RTC Status Register D
• Bit 7: Valid Time/Date (always reads 1)
• Bit 6: Reserved
• Bits 5-0: RTC Alarm Day of the Month
Note RTC registers that are not listed above are used by the BIOS and should be considered “Reserved”.
Altering the contents of any unlisted RTC register may interfere with the operation of your cpuModule.
The specific uses of the unlisted RTC registers will depend on the BIOS version loaded on the cpuModule.
Contact RTD's technical support for more information.
Table 52 Real Time Clock Registers
Registers
(hex)
Registers
(decimal)
Function