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参数资料
| 型号： | MM58174 |
| 厂商： | National Semiconductor Corporation |
| 英文描述： | Microprocessor-Compatible Real-Time Clock |
| 中文描述： | 微处理器兼容实时时钟 |
| 文件页数： | 5/8页 |
| 文件大小： | 130K |
| 代理商： | MM58174 |
Circuit Description
(Continued)
TABLE IIa. Interrupt Selection Data
Mode: Address 15, Write Mode
Function
DB3
DB2
DB1
DB0
No Interrupt
Int. at 60 Sec. Intervals
*
Int. at 5.0 Sec. Intervals
*
Int. at 0.5 Sec. Intervals
*
X
0
1
0
0
0
0
1
0
0
0
0
1
0/1
0/1
0/1
*
a
16.6 ms
DB3
e
0, single interrupt
DB3
e
1, repeated interrupt
TABLE IIb. Interrupt Read Back (Status)
Mode: Address 15, Read Mode
Interrupt Status
DB3
DB2
DB1
DB0
Reset
60 Sec. Signal
5.0 Sec. Signal
0.5 Sec. Signal
X
X
X
X
0
1
0
0
0
0
1
0
0
0
0
1
X
e
don’t care state
TABLE III. Years Status Register
Mode: Address 13, Write Mode
DB3
DB2
DB1
DB0
Leap Year
Leap Year-1
Leap Year-2
Leap Year-3
1
0
0
0
0
1
0
0
0
0
1
0
0
0
0
1
Note:
Leap year counter rolls over on December 31
@
23:59:59.
INTERRUPT SYSTEM
The interrupt output and its frequency of operation is en-
abled by writing to address 15 (see Table IIa). To ensure
correct operation, the interrupt should be serviced within
16.6 ms.
The interrupt is initialized by writing ‘‘0’’ to address 15 and
reading the interrupt, i.e., reading at address 15 three times.
Initialization must be performed at power on and also if the
interrupt is not serviced correctly within 16.6 ms.
SERVICING THE INTERRUPT
In a typical system the open drain interrupt output is wired to
the processor interrupt system. Hence, when the interrupt
timer times out, the interrupt output is pulled low and the
processor is interrupted.
The processor may then reset the interrupt by utilizing the
following procedure:
Read Address 15 three times.
This resets the interrupt output and restarts the interrupt
timer when in the repeat mode.
It is recommended that the interrupt output is connected to
a unique processor port.
CRYSTAL PARAMETERS
Figure 4 is an electrical representation of the crystal along
with some typical values. The 32.768 kHz crystal is an NT
CUT (tuning fork type) or XY BAR for use in a parallel reso-
nant Pierce oscillator.
TL/F/6681–5
C
1
&
0.003 pF
C
0
&
3.0 pF
R
S
&
35 k
X
FIGURE 4. Typical Crystal Parameters
DEVICE INITIALIZATION AND OSCILLATOR SETTING
When first installed or if the battery back-up has failed, the
MM58174A will require to be properly initialized. The follow-
ing sequence is a suggested flow of operations to achieve
this.
Action
Result
1) Apply power.
Clears interrupt timer
chain.
2) Write ‘‘0’’ to address 15.
3) Read 3 times from
address 15.
Clears interrupt output
logic.
4) Write ‘‘0’’ on DB3 to
address 0.
Clears test mode.
5) Write ‘‘0’’ on DB0 to
address 14.
Stops clock running.
6) Set up timekeeping
registers.
Load real-time into device
time registers, minutes to
leap years.
7) Write ‘‘1’’ on DB0 to
address 14.
Starts timekeeping
synchronized to an
external time source.
8) Program and start
interrupts.
Commence interrupt
timing, if so required.
OSCILLATOR SETTING
Directly connecting a frequency meter to the Crystal Out pin
(14) will not allow correct frequency setting because of the
extra capacitive loading of the meter. One possibility for set-
ting is to use a high impedance probe or a CMOS buffer to
keep the loading as low as possible (e.g., 100 x 2 pF probe).
Alternatively, a buffered output of 16.384 kHz OSC/2 can
be produced on DB0 by applying the following procedure:
Action
Result
1) Write a ‘‘1’’ on DB3 to
address 0.
Selects test mode.
2) Write a ‘‘1’’ on DB0 to
address 14.
Starts clock timing.
3) Read at address 1 (tenths
of secs).
‘‘Data Changed’’ signal is
read.
4) Read at address 1 and
HOLD the strobe LOW.
16.384 kHz appears on
DB0.
5) Adjust trimmer capacitor.
There must be no extra activity on the RD line between
steps 3 and 4 or only the normal ‘‘Data Changed’’ signal will
be observed on the data bus. Thus if the normal host proc-
essor system is being used to generate the chip waveforms,
proper care must be taken.
5
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|---|---|
| MM58174A | Microprocessor-Compatible Real-Time Clock |
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相关代理商/技术参数 |
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|---|---|
| MM58174A | 制造商:NSC 制造商全称:National Semiconductor 功能描述:Microprocessor-Compatible Real-Time Clock |
| MM58174AN | 制造商:NSC 制造商全称:National Semiconductor 功能描述:Microprocessor-Compatible Real-Time Clock |
| MM58201 | 制造商:NSC 制造商全称:National Semiconductor 功能描述:Multiplexed LCD Driver |
| MM58241 | 制造商:NSC 制造商全称:National Semiconductor 功能描述:MM58241 High Voltage Display Driver |
| MM58241N | 制造商:NSC 制造商全称:National Semiconductor 功能描述:MM58241 High Voltage Display Driver |
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