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参数资料
| 型号： | MM58174AN |
| 厂商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分类： | XO, clock |
| 英文描述： | Microprocessor-Compatible Real-Time Clock |
| 中文描述： | 0 TIMER(S), REAL TIME CLOCK, PDIP16 |
| 封装： | 0.300 INCH, PLASTIC, DIP-16 |
| 文件页数： | 3/8页 |
| 文件大小： | 130K |
| 代理商： | MM58174AN |
Functional Description
The MM58174 is a microprocessor bus-oriented real-time
clock. The circuit includes addressable real-time counters
for tenths of seconds through months and a write only regis-
ter for leap year calculation. The counters are arranged as
bytes of four bits each. When addressed a byte will appear
on the data I/O bus so that each word can be accessed
independently. If any byte does not contain four bits (e.g.,
days of the week uses only 3 bits), the unused bits will be
unrecognized during a write operation and tied to V
SS
during
a read operation.
The addressable reset latch causes the pre-scaler, tenths of
seconds, seconds, and tens of seconds to be held in a reset
condition. If a register is updated during a read operation the
I/O data is prevented from updating and a subsequent read
will return the illegal b.c.d. code ’1111’. The interrupt timer
may be programmed for intervals of 0.5 second, 5 seconds,
or 60 seconds and may be coded as a single or repeated
operation. The open drain interrupt output is pulled to V
SS
when the timer times out and reading the interrupt register
provides the internal selected information.
Circuit Description
The block diagram shown inFigure 1 shows the structure of
the CMOS clock chip. A 16-pin DIL package is used.
CRYSTAL OSCILLATOR
This consists of a CMOS inverter/amplifier with on-chip bias
resistor and capacitors. A single 6 pF–36 pF trimmer is all
that is required to fine tune the crystal (see Figure 2). How-
ever, for improved stability, some crystals may require a ca-
pacitor of typical value 20 pF to be added between pin 14
and ground. The output of the oscillator is blocked by the
start/stop F/F.
NON-INTEGER DIVIDER
This counter divides the incoming 32,768 Hz frequency by
15/16 down to 30,720 Hz.
FIXED DIVIDER (512)
This is a standard 9-stage binary ripple counter. Output fre-
quency is 60 Hz. This counter is reset to zero by start/stop
F/F.
FIXED DIVIDER (6)
This is a 3-stage Johnson counter with a 10 Hz output sig-
nal. This counter is reset to zero state by the start/stop F/F.
SYNCHRONIZATION STAGE
Both 10 Hz and 32,768 Hz clocks are fed into this section. It
is used to generate a pulse of 15.25
m
s width on the rising
edge of each 10 Hz pulse.
This pulse is used to increment all the seconds, minutes,
hours, days, months, and year counter and also to set the
data changed F/F.
DATA CHANGED F/F
This is set by the rising edge of each 10 Hz pulse to indicate
that the clock value has changed since the last read opera-
tion. It is reset by any clock read command.
The flip flop sets all data bus bits to a ‘‘1’’ during RD time
indicating that a register has been updated. This transient
condition may occur at the end of the Read Data strobe.
Hence, invalid data may still be read from the clock, if the
strobe width was less than 3
m
s.
Connection Diagram
Dual-In-Line Package
TL/F/6681–2
Top View
Order Number MM58174AN
See NS Package Number N16A
The possibility may be overcome by implementing a further
read of the tenths of seconds register at the end of every
series of reads (starting with a read at the tenths of seconds
register) and checking for unchanged data.
SECONDS COUNTERS
There are three counters for Seconds:
a) tenths of seconds
b) units of seconds
c) tens of seconds
The outputs of all three counters can be separately multi-
plexed on to the command 4-bit output bus. Table I shows
the address decoding for each counter. All three counters
are reset to zero by the start/stop F/F.
MINUTES COUNTERS
There are two Minutes counters:
a) units of minutes
b) tens of minutes
Both counters are parallel loaded with data from the 4-bit
input bus when addressed by the microprocessor and a
Write Data Strobe pulse given. Similarly, the output of both
counters can be read separately onto the common 4-bit out-
put bus (Table I).
HOURS COUNTERS
There are two Hours counters which will count in a 24-hour
mode:
a) units of hours
b) tens of hours
Both counters have identical parallel load and read multi-
plex features to the Minutes counters.
SEVEN DAY COUNTER
There is a 7-state counter which increments every 24 hours.
It will have identical parallel load and read multiplex capabili-
ties to the Minutes and Hours counters. The counter counts
cyclically from 1–7.
3
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| MM58201 | 制造商:NSC 制造商全称:National Semiconductor 功能描述:Multiplexed LCD Driver |
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