FDC37C935-QS Standard Microsystems (SMSC), FDC37C935-QS Datasheet - Page 129

• Manufacturer Part Number: FDC37C935-QS
• Manufacturer: Standard Microsystems (SMSC)

Specifications of FDC37C935-QS

• Lead Free Status / RoHS Status: Supplier Unconfirmed

Time Calendar and Alarm
The processor program obtains time and
calendar information by reading the appropriate
locations. The program may initialize the time,
calendar and alarm by writing to these locations.
The contents of the ten time, calendar and
alarm bytes can be in binary or BCD as shown
in Table 57.
Before initializing the internal registers, the SET
bit in Register B should be set to a "1" to prevent
time/calendar updates from occurring. The
program initializes the ten locations in the binary
or BCD format as defined by the DM bit in
Register B.The SET bit may now be cleared to
allow updates.
The 12/24 bit in Register B establishes whether
the hour locations represent 1 to 12 or 0 to 23.
The 12/24 bit cannot be changed without
reinitializing the hour locations. When the 12
hour format is selected, the high order bit of the
hours byte represents PM when it is a "1".
Once per second, the ten time, calendar and
alarm bytes are switched to the update logic
129
an alarm condition. If any of the ten bytes are
read at this
undefined. The update cycle time is shown in
Table 58. The update logic contains circuitry for
automatic end-of-month recognition as well as
automatic leap year compensation.
The three alarm bytes may be used in two ways.
First, when the program inserts an alarm time in
the appropriate hours, minutes and seconds
alarm locations, the alarm interrupt is initiated at
the specified time each day if the alarm enable
bit is high. The second usage is to insert a "don't
care" state in one or more of three alarm bytes.
The "don't care" code is any hexadecimal byte
from C0 to FF inclusive. That is the two most
significant bits of each byte, when set to "1"
create a "don't care" situation. An alarm
interrupt each hour is created with a "don't care"
code in the hours alarm location. Similarly, an
alarm is generated every minute with "don't
care" codes in the hours and minutes alarm
bytes. The "don't care" codes in all three alarm
bytes create an interrupt every second.
time, the data outputs are