Functional Description (Continued)
MAIN STATUS REGISTER
backed mode. Bit D6 is automatically set to 1 on initial pow-
er-up or an oscillator fail event. The oscillator fail flag is
reset by writing a one to the clock start/stop bit in the Real
Time Mode Register, with the crystal oscillating.
When D6 is written to, it defines whether the TCP is being
used in battery backed (normal) or in a single supply mode
application. When set to a one this bit configures the TCP
for single power supply applications. This bit is automatically
set on initial power-up or an oscillator fail event. When set,
D6 disables the oscillator reference circuit. The result is that
the oscillator is referenced to V . When a zero is written to
CC
D6 the oscillator reference is enabled, thus the oscillator is
TL/F/9981–12
The Main Status Register is always located at address 0
regardless of the register block selected.
referenced to V . This allows operation in standard battery
BB
standby applications.
D0: This read only bit is a general interrupt status bit that is
taken directly from the interrupt pins. The bit is a one when
an interrupt is pending on either the INTR pin or the MFO
pin (when configured as an interrupt). This is unlike D3
which can be set by an internal event but may not cause an
interrupt. This bit is reset when the interrupt status bits in the
Main Status Register are cleared.
At initial power on, if the DP8573A is going to be pro-
pin should be
grammed for battery backed mode, the V
BB
connected to a potential in the range of 2.2V to V
0.4V.
b
CC
For single supply mode operation, the V pin should be
BB
connected to GND and the PFAIL pin connected to V
.
CC
D7: Writing a one to this bit enables the test mode register
at location 1F (see Table III). This bit should be forced to
zero during initialization for normal operation. If the test
mode has been entered, clear the test mode register before
leaving test mode. (See separate test mode application
note for further details.)
D1–D3: These three bits of the Main Status Register are the
main interrupt status bits. Any bit may be a one when any of
the interrupts are pending. Once an interrupt is asserted the
mP will read this register to determine the cause. These
interrupt status bits are not reset when read. Except for D1,
to reset an interrupt a one is written back to the correspond-
ing bit that is being tested. D1 is reset whenever the PFAIL
TIME SAVE CONTROL REGISTER
e
pin
logic 1. This prevents loss of interrupt status when
reading the register in a polled mode. D1 and D3 are set
regardless of whether these interrupts are masked or not by
bits D6 and D7 of Interrupt Control Registers 0 and 1.
D4, D5 and D7: General purpose RAM bits.
D6: Bit D6 controls the register block to be accessed (see
memory map).
PERIODIC FLAG REGISTER
TL/F/9981–14
D0–D5: General purpose RAM bits.
D6: Not Available, appears as logic 0 when read.
D7: Time Save Enable bit controls the loading of real-time-
clock data into the Time Save RAM. When a one is written
to this bit the Time Save RAM will follow the corresponding
clock registers, and when a zero is written to this bit the time
in the Time Save RAM is frozen. This eliminates any syn-
chronization problems when reading the clock, thus negat-
ing the need to check for a counter rollover during a read
cycle.
TL/F/9981–13
The Periodic Flag Register has the same bit for bit corre-
spondence as Interrupt Control Register 0 except for D6
and D7. For normal operation (i.e., not a single supply appli-
cation) this register must be written to on initial power up or
after an oscillator fail event. D0–D5 are read only bits, D6
and D7 are read/write.
This bit must be set to a one prior to power failing to enable
the Time Save feature. When the power fails this bit is auto-
matically reset and the time is saved in the Time Save RAM.
REAL TIME MODE REGISTER
D0–D5: These bits are set by the real time rollover events:
e
read and can be used as selective data change flags.
(Time Change
1). The bits are reset when the register is
D6: This bit performs a dual function. When this bit is read, a
one indicates that an oscillator failure has occurred and the
time information may have been lost. Some of the ways an
oscillator failure might be caused are: failure of the crystal,
shorting OSC IN or OSC OUT to GND or V , removal of
CC
crystal, removal of battery when in the battery backed mode
(when a ‘‘0’’ is written to D6), lowering the voltage at the
V
pin to a value less than 2.2V when in the battery
BB
TL/F/9981–15
11
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