RTC - 72421 / 72423

4-BIT PARALLEL INTERFACE REAL TIME CLOCK MODULE

RTC - 72421 / 72423

•Built-in crystal unit removes need for adjustment and reduces installation costs

•Microprocessor bus compatible ( tWW, tRD = 120 ns )•Use of C-MOS IC enables low current consumption ( 5 ∝ A Max., at VDD = 2.0 V )•Compatibility with Intel CPU bus•Address latch enable (ALE) pin compatible with multiplex bus CPUs•Time (hours, minutes, seconds) and calendar (year, month, day) counter•24-hour/12-hour switchover and automatic leap-year correction functions•Fixed-period interrupt function•30-seconds correction (adjustment) function•Stop, start, and reset functions•Battery back-up function•Same mounting conditions as general-purpose SMD ICs possible (RTC-72423)∗Pins and functions compatible with the SMC-5242 series

„Overview

The RTC-72421/RTC-72423 module is a real time clock that can be connected directly to a microprocessor's bus. Its built-in crystal unit enables highly accurate time-keeping with no physical access required for adjustment and, since there is no need to connect external components, mounting and other costs can be reduced.

In addition to its time and calendar functions, the RTC-72421/RTC-72423 enables the use of 30-seconds correction and fixed- period interrupt functions.

The RTC-72421/RTC-72423 module is ideally suited for applications requiring timing management, such as personal computers, dedicated word-processors, fax machines, multi-function telephones, and sequencers.

„Block diagram

 

 

 

 

 

 

 

RTC-72421/72423

 

 

OSC

Counter

 

 

 

 

 

D3

 

RESET

STOP

 

HOLD

BUSY

 

 

 

D2

Gate

 

 

 

 

bit

bit

 

bit

bit

 

24/12

D1

 

 

 

30sec ADJ

 

 

 

 

 

bit

 

D0

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

bit

 

 

 

 

 

 

 

WR

 

 

S1

S10

MI1

MI10

H1

H10

W

Gate

 

 

 

 

 

 

 

 

RD

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

A3

 

S1 to CF

 

 

 

 

 

 

 

A2

 

D1

D10

MO1

MO10

Y1

Y10

 

A1

Latch

Decoder

 

 

 

 

 

 

 

 

A0

 

 

 

 

 

 

 

 

 

CS0

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Output Selector

ALE

 

 

 

 

 

 

 

 

STD.P

 

 

 

 

 

 

 

 

64 Hz

CS1

 

 

 

 

 

 

 

 

 

 

 

 

 

 

1 Second carry

 

 

 

 

 

 

 

 

 

 

 

 

CD

 

CE

CF

1 Minute carry

 

 

 

 

 

1 Hour carry

 

 

 

 

 

 

 

 

 

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