Compaq 850 manual RTC Control Register A, Byte 0Ah

Technical Reference Guide

RTC Control Register A, Byte 0Ah

Bit	Function
7	Update in Progress. Read only.
	0 = Time update will not occur before 2444 us
	1 = Time update will occur within 2444 us
6..4	Divider Chain Control. R/W.
	00x = Oscillator disabled.
	010 = Normal operation (time base frequency = 32.768 KHz).
	11x = Divider chain reset.
3..0	Periodic Interrupt Control. R/W. Specifies the periodic interrupt interval.
	0000	= none	1000 = 3.90625 ms
	0001	= 3.90625 ms	1001 = 7.8125 ms
	0010	= 7.8125 ms	1010 = 15. 625 ms
	0011	= 122.070 us	1011	= 31.25 ms
	0100	= 244.141 us	1100	= 62.50 ms
	0101	= 488.281 us	1101	= 125 ms
	0110	= 976.562 us	1110	= 250 ms
	0111	= 1.953125 ms	1111	= 500 ms

RTC Control Register B, Byte 0Bh

Bit	Function
7	Time Update Enable/disable
	0	= Normal operation, 1 = Disable time updating for time set
6	Periodic Interrupt Enable/Disable.
	0	= Disable,	1 = Enable interval specified by Register A
5	Alarm Interrupt Enable/disable
	0	= Disabled,	1 = Enabled
4	End-of-Update Interrupt Enable/Disable
	0	= Disabled,	1 = Enabled
3	Reserved (read 0)
2	Time/Date Format Select
	0	= BCD format,		1 = Binary format
1	Time Mode
	0	= 12-hour mode,		1 = 24-hour mode

0Automatic Daylight Savings Time Enable/Disable

0= Disable

1= Enable (Advance 1 hour on 1st Sunday in April, retreat 1 hour on last Sunday in October).

RTC Status Register C, Byte 0Ch

Bit Function

7If set, interrupt output signal active (read only)

6If set, indicates periodic interrupt flag

5If set, indicates alarm interrupt

4If set, indicates end-of-update interrupt

3..0 Reserved

RTC Status Register D, Byte 0Dh

Bit	Function
7	RTC Power Status
	0	= RTC has lost power
	1	= RTC has not lost power
6..0	Reserved

Compaq Deskpro EXS and Workstation 300 Personal Computers 4-23

Featuring the Intel Pentium 4 Processor

First Edition - December 2000