fm3808 Ramtron Corporation, fm3808 Datasheet - Page 10

• Manufacturer Part Number: fm3808
• Description: 256kb Bytewide Fram W/ Real-time Clock
• Manufacturer: Ramtron Corporation

Supervisor Operation
The Supervisor function includes a clock/calendar
alarm, a watchdog timer, and a power monitor. A
programmable interrupt pin (INT) provides maximum
flexibility to the system designer. The INT pin is
designed to allow either reset or interrupt capability
to the host processor.
Alarm
The alarm function compares user-programmed
values to the corresponding time-of-day values. When
a match occurs, the alarm event occurs. The alarm
drives an internal flag AF (7FF0 bit D6) and may
drive the INT pin if desired.
There are four alarm match fields. They are Date,
Hours, Minutes, and Seconds. Each of these fields
also has a Match bit that is used to determine if the
field is used in the alarm match logic. Setting the
Match bit to ‘0’ indicates that the corresponding field
will be used in the match process.
Depending on the Match bits, the alarm can occur as
specifically as one particular second on one day of
the month, or as frequently as once per second
continuously. The MSB of each Alarm register is a
Alarm Match Bit Examples
Seconds
1
0
0
0
0
Rev. 1.3 (EOL)
Feb. 2006
Minutes
1
1
0
0
0
Hours
1
1
1
0
0
Date
1
1
1
1
0
Alarm condition
No match required = alarm 1/second
Alarm when seconds match, = alarm 1/minute
Alarm when seconds, minutes match, = alarm 1/hour
Alarm when seconds, minutes, hours match, = alarm 1/day
Alarm when seconds, minutes, hours, date match, = alarm 1/month
Match bit. Examples of the Match bit settings are
shown in the table below. Selecting none of the match
bits (all ‘1’s) indicates that no match is required. The
alarm occurs every second. Setting the match select
bit for seconds to ‘0’ causes the logic to match the
seconds alarm value to the current time of day. Since
a match will occur for only one value per minute, the
alarm occurs once per minute. Likewise setting the
seconds and minutes match select bits causes an exact
match of these values. Thus, an alarm will occur once
per hour. Setting seconds, minutes, and hours causes
a match once per day. Lastly, selecting all match-
values causes an exact time and date match. Selecting
other bit combinations will not produce meaningful
results, however the alarm circuit should follow the
functions described.
There are two ways a user can detect an alarm event,
by reading the AF flag or monitoring the INT pin.
The AF flag in the register 7FF0h (bit D6) will
indicate that a date/time match has occurred. The AF
bit will be set to 1 when a match occurs. Reading the
Flags/Control register clears the alarm flag bit (and
all others). A hardware interrupt pin may be used to
detect an alarm event. The AIE bit in the register
7FF6h The interrupt function is described below.
Page 10 of 27
FM3808