m48t86 STMicroelectronics, m48t86 Datasheet - Page 18

• Manufacturer Part Number: m48t86
• Description: 5v Pc Real Time Clock
• Manufacturer: STMicroelectronics

Square wave output selection
18/36
should avoid interrupt service routines that would cause the time needed to read valid
time/calendar data to exceed 244µs.
The third method uses a periodic interrupt to determine if an update cycle is in progress.
The UIP Bit is set high between the setting of the PF Bit (Register C; Bit 6). Periodic
interrupts that occur at a rate greater than t
reached at each occurrence of the periodic interrupt.The READs should be completed
within 1/(t
Thirteen of the 15 divider taps are made available to a 1-of-15 selector, as shown in the
block diagram of
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
SQW frequency selection shares the 1-of-15 selector 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) Bit.
Table 4.
RS3
0
0
0
0
0
0
0
0
1
1
1
1
1
1
1
1
PL/2
Square wave frequency/periodic interrupt rate
+ t
RS2
Register A bits
0
0
0
0
1
1
1
1
0
0
0
0
1
1
1
1
BUC
Figure 4 on page
) to ensure that data is not read during the update cycle.
RS1
0
0
1
1
0
0
1
1
0
0
1
1
0
0
1
1
8. The purpose of selecting a divider tap is to generate a
RS0
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
BUC
Frequency
allow valid time and date information to be
8.192
4.096
2.048
1.024
None
256
128
512
256
128
64
32
16
8
4
2
Square wave
Units
kHz
kHz
kHz
kHz
Hz
Hz
Hz
Hz
Hz
Hz
Hz
Hz
Hz
Hz
Hz
Table 4 on page
976.5625
1.953125
3.90625
122.070
244.141
488.281
3.90625
Period
7.8125
7.8125
15.625
Periodic interrupt
31.25
None
62.5
125
250
500
18. The
Units
ms
ms
ms
ms
ms
ms
ms
ms
ms
ms
ms
us
us
us
us