LPC47S457-NC SMSC [SMSC Corporation], LPC47S457-NC Datasheet - Page 101

• Manufacturer Part Number: LPC47S457-NC
• Description: Advanced I/O with X-Bus Interface
• Manufacturer: SMSC [SMSC Corporation]

RS3-0
The four rate selection bits select one of 15 taps on the divider chain or disable the divider output. The selected tap
determines rate or frequency of the periodic interrupt. The program may enable or disable the interrupt with the PIE
bit in Register B.
with the RS0-RS3 bits. These four bits are read/write bits that are not affected by VTR POR.
Register B
SET
When the SET bit is a "0", the update functions normally by advancing the counts 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 VTR
POR or any internal functions.
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
SMSC DS – LPC47S45x
Table 51 lists the periodic interrupt rates and equivalent output frequencies that may be chosen
OSCILLATOR
FREQUENCY
32.768 kHz
32.768 kHz
32.768 kHz
32.768 kHz
32.768 kHz
32.768 kHz
RATE SELECT
RS3 RS2 RS1 RS0
0 0 0 0
0 0 0 1
0 0 1 0
0 0 1 1
0 1 0 0
0 1 0 1
0 1 1 0
0 1 1 1
1 0 0 0
1 0 0 1
1 0 1 0
1 0 1 1
1 1 0 0
1 1 0 1
1 1 1 0
1 1 1 1
SET
B7
PIE
B6
Table 51 − RTC Periodic Interrupt Rates
Table 50 − RTC Divider Selection Bits
DV2
0
0
0
0
1
1
AIE
REGISTER A BITS
B5
DATASHEET
UIE
Page 101 of 259
DV1
B4
32.768 kHz TIME BASE
PERIOD
OF INTERRUPT
0.0
3.90625 ms
7.8125 ms
122.070 μs
244.141 μs
488.281 μs
976.562 μs
1.953125 ms
3.90625 ms
7.8125 ms
15.625 ms
31.25 ms
62.5 ms
125 ms
250 ms
500 ms
0
0
1
1
0
1
RES
B3
DV0
X
X
0
1
0
1
RATE
DM
B2
Normal Operate
Reset Divider
Normal Operate
Test
Test
Reset Divider
FREQUENCY
OF INTERRUPT
256 Hz
128 Hz
8.192 Hz
4.096 kHz
2.048 kHz
1.024 kHz
512 Hz
256 Hz
128 Hz
64 Hz
32 Hz
16 Hz
8 Hz
4 Hz
2 Hz
24/12
B1
MODE
DSE
B0
Rev. 07/09/2001