IBM BDM-610000049 User Manual

Page 80

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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: I

RQ 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

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