Xycom XVME-113, User Manual

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Chapter 3 – Real Time Clock
3-6
3.4.3
Day of Week Counter Register (RTC Register 09h)
The Day of Week Counter Register is used to set or read the day of the week. The day is encoded with a value from 0
to 6, according to the following chart.
Data 0 1 2 3 4 5 6
Day of Week Sun. Mon. Tue. Wed. Thu. Fri. Sat.
3.4.4 Day, Month, and Year Counter Registers (RTC Registers 0Bh, 0Dh, 0Fh)
These registers are used to set or read the RTC calendar date. Each of these registers is encoded in BCD format. For
example, the 25th day of the month would be encoded in the Day Counter Register as '00100101'.
Only the last two digits of the year are used. Leap years are automatically recognized (Note: A year whose last two digits
are a multiple of four is recognized as a leap year).
3.4.5
64 Hz Alarm - Day Alarm Registers (RTC Registers 11h through 1Bh)
These registers are used to set the time at which the RTC triggers an alarm condition. Bit 7 of each of these registers
is the register's enable (ENB) bit. If an alarm register's ENB bit is set, the RTC uses that register in its comparison to
its corresponding counter register to determine if the alarm time has been reached. Two or more alarm registers may
be enabled at a time. When the values in the counter registers match the corresponding values in the enabled alarm
registers, the alarm condition is met. This can be thought of as a logical AND of the alarm registers that are enabled.
The RTC then sets the Alarm Flag (AF) bit in Control Register A. Since interrupts from the RTC are not used on the
XVME-113, the AF bit is the only indication to the host processor that the alarm time has been reached.
3.4.6
Control Register A (RTC Register 1Dh)
CF * * CIE AIE * * AF
The only bits that are used in this register are the CF and the AF bits. Since interrupts from the RTC are not used on the
XVME-113, the Carry Interrupt Enable (CIE) and Alarm Interrupt Enable (AIE) bits are unused and should always be
written as '0'.