
SMSC DS – FDC37N958FR
Page 217
Rev. 09/01/99
REGISTER B (BH)
B7
SET
B6
PIE
B5
AIE
B4
UIE
B3
RES
B2
DM
B1
24/12
B0
DSE
SET
When the SET bit is a "0", the update functions
normally
by
advancing
once-per-second. When the SET bit is a "1", an
update cycle in progress is aborted and the
program may initialize the time and calendar
bytes without an update occurring in the middle
of initialization. SET is a read/write bit which is
not modified by VCC1 POR or any internal
functions.
the
counts
PIE
The periodic interrupt enable bit is a read/write
bit which allows the periodic-interrupt flag (PF)
bit in Register C to cause the IRQB port to be
driven low. The program writes a "1" to the PIE
bit in order to receive periodic interrupts at the
rate specified by the RS3 - RS0 bits in Register
A. A “0” in PIE blocks IRQB from being initiated
by a periodic interrupt, but the periodic flag (PF)
is still set at the periodic rate. PIE is not
modified by any internal function, but is cleared
to "0" by a VCC1 POR.
AIE
The alarm interrupt enable bit is a read/write bit,
which when set to a "1" permits the alarm flag
(AF) bit in Register C to assert IRQB. An
alarm interrupt occurs for each second that the
three time bytes equal the three alarm bytes
(including a "don't care" alarm code of binary
11XXXXXX). When the AIE bit is a "0", the AF
bit does not initiate an IRQB signal. The VCC1
POR port clears AIE to "0". The AIE bit is not
affected by any internal functions.
UIE
The update-ended interrupt enable bit is a
read/write bit which enables the update-end flag
(UF) bit in Register C to assert IRQB. The
VCC1 POR port or the SET bit going high clears
the UIE bit.
RES
Reserved - read as zero
DM
The data mode bit indicates whether time and
calendar updates are to use binary or BCD
formats. The DM bit is written by the processor
program and may be read by the program, but
is not modified by any internal functions or by
VCC1 POR. A "1" in DM signifies binary data,
while a "0" in DM specifies BCD data.
24/12
The 24/12 control bit establishes the format of
the hours byte as either the 24 hour mode if set
to a "1", or the 12 hour mode if cleared to a
"0". This is a read/write bit which is not affected
by VCC1 POR or any internal function.
DSE
The daylight savings enable bit is read only and
is always set to a "0" to indicate that the
daylight savings time option is not available.