M48T86 Datasheet, PDF (12/23 Pages) STMicroelectronics – 5V PC REAL TIME CLOCK

M48T86
Figure 11. Address Map
0
00
14
BYTES
CLOCK AND CONTROL
STATUS REGISTERS
13
0D
14
0E
114
BYTES
STORAGE REGISTERS
127
7F
0
SECONDS
1
SECONDS ALARM
2
MINUTES
3
MINUTES ALARM
4
HOURS
5
HOURS ALARM
6
DAY OF WEEK
7
DATE OF MONTH
8
MONTH
9
YEAR
10
REGISTER A
11
REGISTER B
12
REGISTER C
13
REGISTER D
BCD OR
BINARY
FORMAT
AI01650
UPDATE CYCLE INTERRUPT
After each update cycle, the update cycle ended
flag bit (UF) (Register C; Bit 4) is set to a "1". If the
update interrupt enable bit (UIE) (Register B; Bit 4)
is set to a "1", and the SET bit (Register B; Bit 7) is
a "0", then an interrupt request is generated at the
end of each update cycle.
SQUARE WAVE OUTPUT SELECTION
Thirteen of the 15 divider taps are made available
to a 1-of-15 selector, as shown in the block dia-
gram of Figure 3. The purpose of selecting a divid-
er tap is to generate a square wave output signal
on the SQW pin. The RS3-RS0 bits in Register A
establish the square wave output frequency.
These frequencies are listed in Table 10. The
SQW frequency selection shares the 1-of-15 se-
lector with the periodic interrupt generator. Once
the frequency is selected, the output of the SQW
pin can be turned on and off under program control
with the square wave enabled (SQWE).
OSCILLATOR CONTROL BITS
When the M48T86 is shipped from the factory the
internal oscillator is turned off. This feature pre-
vents the lithium energy cell from being dis-
charged until it is installed in a system. A pattern of
"010" in Bits 4-6 of Register A will turn the oscilla-
tor on and enable the countdown chain. A pattern
of "11X" will turn the oscillator on, but holds the
countdown chain of the oscillator in reset. All other
combinations of Bits 4-6 keep the oscillator off.
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