Overview; Block Diagram - Epson RTC-72421 A Applications Manual

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, t
Use of C-MOS IC enables low current consumption ( 5 A Max., at 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

D3
D2
Gate
D1
D0
WR
Gate
RD
A3
A2
A1 Latch
A0
CS0
ALE
CS1
= 120 ns )
RD
OSC Counter
RESET STOP
bit bit
30sec ADJ
bit
S1 S10
S1 to CF
D1 D10
Decoder
CD
Page - 1
= 2.0 V )
DD
RTC-72421/72423
HOLD BUSY
bit bit 24/12
bit
MI1 MI10 H1 H10
MO1 MO10 Y1 Y10
64 Hz
1 Second carry
1 Minute carry
CE CF
1 Hour carry
W
Output Selector
MQ - 162 - 03
STD.P