AMD SC3200 Index 0Ch RTC Control Register C CRC RO, Index Programmable Century Register CEN R/W

SuperI/O Module 32581C

Table 5-20. RTC Registers (Continued)

Bit Description

3Reserved. This bit is defined as “Square Wave Enable” by the MC146818 and is not supported by the RTC. This bit is always read as 0.

2Data Mode. This bit is reset at VPP power-up reset only.

0:Enable BCD format.

1:Enable Binary format.

1Hour Mode. This bit is reset at VPP power-up reset only.

0:Enable 12-hour format.

1:Enable 24-hour format.

0Daylight Saving. This bit is reset at VPP power-up reset only.

0:Disable.

1:Enable:

-In the spring, time advances from1:59:59 AM to 3:00:00 AM on the first Sunday in April.

-In the fall, time returns from 1:59:59 AM to 1:00:00 AM on the last Sunday in October.

Index 0Ch RTC Control Register C - CRC (RO) Reset Type: Bit Specific

7IRQ Flag. Mirrors the value on the interrupt output signal. When interrupt is active, IRQF is 1. To clear this bit (and deacti- vate the interrupt pin), read the CRC Register as the flag bits UF, AF and PF are cleared after reading this register.

0:IRQ inactive.

1:Logic equation is true: ((UIE and UF) or (AIE and AF) or (PIE and PF)).

6Periodic Interrupt Flag. Cleared to 0 on RTC reset (i.e., hardware or software reset) or the RTC disabled. In addition, this bit is cleared to 0 when this register is read.

0:No transition occurred on the selected tap since the last read.

1:Transition occurred on the selected tap of the divider chain.

5Alarm Interrupt Flag. Cleared to 0 as long as bit 7 of the CRD Register is reads 0. In addition, this bit is cleared to 0 when this register is read.

0:No alarm detected since the last read.

1:Alarm condition detected.

4Update Ended Interrupt Flag. Cleared to 0 on RTC reset (i.e., hardware or software reset) or the RTC disabled. In addi- tion, this bit is cleared to 0 when this register is read.

0:No update occurred since the last read.

1:Time registers updated.

3:0	Reserved.
Index 0Dh	RTC Control Register D - CRD (RO)	Reset Type: VPP PUR

7Valid RAM and Time. This bit senses the voltage that feeds the RTC (VSB or VBAT) and indicates whether or not it was too low since the last time this bit was read. If it was too low, the RTC contents (time/calendar registers and CMOS RAM) is not valid.

0:The voltage that feeds the RTC was too low.

1:RTC contents (time/calendar registers and CMOS RAM) are valid.

6:0	Reserved.
Index Programmable		Date of Month Alarm Register - DOMA (R/W)	Reset Type: VPP PUR

7:0

Date of Month Alarm Data. Values may be 01 to 31 in BCD format or 01 to 1F in Binary format.

When bits 7 and 6 are both set to one (“11”), unconditional match is selected. (Default)

Index Programmable Month Alarm Register - MONA (R/W) Reset Type: VPP PUR

7:0

Month Alarm Data. Values may be 01 to 12 in BCD format or 01 to 0C in Binary format.

When bits 7 and 6 are both set to one (“11”), unconditional match is selected. (Default)

Index Programmable Century Register - CEN (R/W) Reset Type: VPP PUR

7:0

Century Data. Values may be 00 to 99 in BCD format or 00 to 63 in Binary format.

AMD Geode™ SC3200 Processor Data Book 111