MQ162-03
Application Manual
Real Time Clock Module
RTC-72421/72423
Model
Product Number
RTC-72421 A
RTC-72421 B
RTC-72423 A
RTC-72423
Q4272421x000100
Q4272421x000200
Q4272423x000600
Q4272423x000700
RTC - 72421 / 72423
CONTENTS
„ Overview............................................................................................. 1
„ Block diagram ..................................................................................... 1
„ Terminal connections.......................................................................... 2
„ Terminal functions............................................................................... 3
„ Characteristics .................................................................................... 4
1. Absolute maximum ratings........................................................................................ 4
2. Recommended operating conditions......................................................................... 4
3. Frequency characteristics and current consumption characteristics.......................... 4
4. Electrical characteristics ( DC characteristics ) ......................................................... 4
„ Switching characteristics (AC characteristics) ........................................... 5
1. When ALE is used .................................................................................................... 5
2. When ALE is fixed at VDD......................................................................................... 6
„ Registers............................................................................................. 7
1. Register table............................................................................................................ 7
2. Notes ........................................................................................................................ 7
3. Functions of register bits (overview).......................................................................... 7
4. Setting the fixed-period pulse output mode and fixed-period interrupt mode............. 8
5. Resetting the fixed-period pulse output mode and fixed-period interrupt mode......... 8
„ Register description ............................................................................ 9
1. Timing registers ........................................................................................................ 9
2. CD register (control register D) ............................................................................... 10
3. CE register (control register E)................................................................................ 11
4. CF register (control register F)................................................................................ 13
„ Using the RTC-72421/RTC-72423.....................................................14
1. Power-on procedure (initialization).......................................................................... 14
2. Read/write of S1 to W registers .............................................................................. 16
3. Write to 30-second ADJ bit ..................................................................................... 16
4. Using the CS1 pin ................................................................................................... 17
„ Power supply circuit example.............................................................17
„ Examples of connection to general-purpose microprocessor.............18
„ External dimensions...........................................................................19
„ Marking layout....................................................................................19
„ Reference data ..................................................................................20
„ Application notes................................................................................21
1. Notes on handling................................................................................................... 21
2. Notes on packaging ................................................................................................ 21
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 µA 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
D2
D1
D0
RESET STOP
HOLD
bit
BUSY
bit
Gate
Gate
bit
bit
24/12
bit
30sec ADJ
bit
S1
S10
D10
MI1
MI10
H1
Y1
H10
Y10
W
WR
RD
A3
A2
A1
S1 to CF
D1
MO1 MO10
Decoder
Latch
A0
CS0
Output Selector
ALE
CS1
STD.P
64 Hz
1 Second carry
1 Minute carry
1 Hour carry
CD
CE
CF
Page - 1
MQ - 162 - 03
RTC - 72421 / 72423
„ Terminal connections
RTC-72421
RTC-72423
DD
STD.P
1
2
24
23
22
V
VDD
VDD
STD.P 1
18
17
16
(
(
)
)
0
DD
V
CS
(
)
CS0
ALE
A0
2
3
DD
V
N.C.
ALE
3
4
21 N.C.
(
)
VDD
0
1
A
5
20 CS
4
5
6
7
8
9
15 CS1
14 D0
13 D1
12 D2
11 D3
10 WR
0
N.C.
6
19
D
1
A
7
18 N.C.
17 N.C.
1
A1
N.C.
8
2
A
9
16
15
14
D
D
D
A2
3
2
3
A
10
11
12
A3
RD
GND
13 WR
RD
GND
The (VDD) pins are at the same electrical level as VDD. Do not connect these pins externally. The N.C. pins are not connected
internally. Ground them in order to prevent noise.
Page - 2
MQ - 162 - 03
RTC - 72421 / 72423
„ Terminal functions
Pin No.
RTC-72421 RTC-72423
Input/ou
tput
Function
Signal
Connect these pines to a bi-directional data bus or CPU data bus. Use this bus
to read to and write from the internal counter and registers.
CS1 CS0 RD WR
Mode of D0 to D3
Output mode (read mode)
Input mode (write mode)
Do not use
H
H
H
L
L
L
L
L
H
H
L
L
D0-D3
(Data bus)
Bi-
direction
11−14
14−16, 19
L
H or L
High impedance (back-up mode)
High impedance (RTC not selected)
H
H
H or L
Address input pins used for connection to CPU address, etc. Used to select the
RTC’s internal counter and registers (address selection).
When the RTC is connected to a multiplexed-bus type of CPU, these pines can
also be used in combination with the ALE described below
A0-A3
(Address bus)
5, 7, 9, 10
Input
Input
4−7
Reads in address data and
When the ALE is high, the address data and
When the (through-mode) ALE falls, the address data and
state for internal latching.
state is read into the RTC.
state at that
status are maintained while
CS0
CS0
CS0
point are held. The held address data and
the ALE is low.
CS0
ALE
3
4
(Address Latch Enable)
Address data and CS0 status
ALE
H
Read into the RTC to set address data
Held in the RTC (latched at the trailing edge of the ALE)
L
If the RTC is connected to a CPU that does not have an ALE pin and thus there
is no need to use this ALE pin, fix it to VDD.
Writes the data on D0 to D3 into the register of the address specified by A0 to
WR
A3, at the leading edge of
WR
.
10
8
13
11
Input
Input
(WRite)
Make sure that
and
are never low at the same time.
RD
WR
Output data to D0 to D3 from the register at the address specified by A0 to A3,
while is low.
RD
RD
(ReaD)
Make sure that
and
are never low at the same time.
RD
WR
When CS1 is high and
read and write are enabled.
is low, the RTC’s chip-select function is valid and
CS0
When the RTC is connected to a multiplexed-bus type of CPU,
requires
CS0
CS1, CS
0
15,2
20,2
Input
the operation of the ALE (see the description of the ALE).
(Chip Select)
Use CS1 connected to a power voltage detection circuit. When CS1 is high, the
RTC is enabled; when it is low, the RTC is on standby.
When CS1 goes low, the HOLD and RESET bits in the RTC registers are
cleared to 0.
This is an N-channel open drain output pin.
Depending on the setting of the CE register, a fixed-period interrupt signal and a
pulse signal are output.
The output from this pin cannot be inhibited by the CS1 and
signals.
CS0
Use a load voltage that is less than or equal to VDD. If not using this pin, keep it
open-circuit.
An example of STD.P connection is shown below.
+5 V or VDD
RTC
STD.P
(STanDard Pulse)
At least 2.2 kΩ
1
1
Output
STD.P
If the STD.P output is not be used during standby operation, connecting the pull-
up resister to +5 V provides a reduction in current consumption. If the STD.P
output is to be used even during standby, connect the pull-up resistor to the
RTC’s VDD. In this case, the current consumption will be increased by the
amount of current flowing through the pull-up resistor.
Connect this pin to power source. Supply to 5 V ± 10 % to this pin during normal
operation; at least 2 V during battery back-up operation.
VDD
18
24
12
Connect this pin to ground.
GND
9
These pins are connected internally to VDD. Leave them open circuit.
(VDD)
16, 17
22,23
3, 6, 8,
17, 18, 21
These pins are not connected internally. Ground them.
N.C.
−
Page - 3
MQ - 162 - 03
RTC - 72421 / 72423
„ Characteristics
1. Absolute maximum ratings
Item
Supply voltage
Input voltage
Symbol
Condition
Specification
Unit
V
VDD
Ta=+25 °C
Ta=+25 °C
Ta=+25 °C
RTC-72421
RTC-72423
−0.3 to 7.0
GND−0.3 to VDD+0.3
GND−0.3 to VDD+0.3
−55 to +85
VI
V
Output voltage
VO
V
°C
°C
Storage temperature
TSTG
−55 to +125
2. Recommended operating conditions
Item
Supply voltage
Symbol
Condition
Specification
Unit
VDD
4.5 to 5.5
RTC-72421 ; −10 to +70
RTC-72423 ; −40 to +85
2.0 to 5.5
V
°C
°C
V
Operating temperature
TOPR
No condensation
Data hold voltage
VDH
tCDR
tr
CS1 data hold time
Operation recovery time
See the section on data
hold timing
2.0 Min.
µs
3. Frequency characteristics and current consumption characteristics
Item
Symbol
Condition
Specification
Unit
RTC-72421A
± 10
± 50
± 20
± 50
RTC-72421B
RTC-72423A
RTC-72423
Ta=+25 °C
VDD=5.0 V
Frequency tolerance
∆f/f0
× 10-6
RTC-72421 : −10 °C to +70 °C
(+25 °C reference)
+10 / −120
Operation temperature
RTC-72423 : −40 °C to +85 °C
(+25 °C reference)
+10 / −220
Frequency voltage
characteristics
Ta=+25 °C
VDD=2.0 V to 5.5 V
± 5 Max.
× 10-6 / V
× 10-6 / year
Aging
fa
VDD=5.0 V, Ta=+25 °C
± 5 Max.
Drop test 3 times on a hard board from
0.75 m height, or 29400 m/s2 × 0.2 ms ×
1/2 sin wave × 3 directions
× 10-6
Shock resistance
S.R.
± 10 Max.
IDD1
IDD2
VDD=5.0 V
1.0 Typ.
0.9 Typ.
10 Max.
5 Max.
Ta=+25 °C, CS1=0 V
I/O currents excluded
Current consumption
µA
VDD=2.0 V
4. Electrical characteristics ( DC characteristics )
Item
Symbol
Condition
Applicable pins
Min. Typ. Max.
Unit
High input voltage 1
Low input voltage 1
High input voltage 2
Low input voltage 2
VIH1
VIL1
VIH2
VIL2
All input pins except for
2.2
V
CS1
0.8
4/5VDD
VDD=2.0 V to
5.5 V
CS1
V
1/5VDD
Input pins except for
D0 to D3
Input leakage current 1
ILK1
1/-1
µA
VI=VDD/0 V
Input leakage current 2
Low output voltage 1
High output voltage
ILK2
VOL1
VOH
10/-10
IOL=2.5 mA
IOH=-400 µA
IOL=2.5 mA
VI = VDD / 0 V
D0 to D3
0.4
V
2.4
Low output voltage 2
Off-state leakage current
VOL2
IOFFLK
0.4
STD.P
10/-10
µA
Input pins except for
D0 to D3
Input capacitance
CI
Input
frequency
1 MHz
10
20
pF
Input-output capacitance
CI/O
D0 to D3 and STD.P
Page - 4
MQ - 162 - 03
RTC - 72421 / 72423
„ Switching characteristics (AC characteristics)
1. When ALE is used
Write mode
( VDD=5 V ± 0.5 V, RTC-72421;Ta=−10 °C to +70 °C, RTC-72423;Ta=−40 °C to +85 °C )
Item
Symbol
tSU(CS1)
tSU(A-ALE)
th(ALE-A)
tw(ALE)
Condition
Min.
1000
50
Max.
Unit
CS1 set-up time
Address set-up time before ALE
Address hold time after ALE
ALE pulse width
50
80
ALE set-up time before write
Write pulse width
tSU(ALE-W)
tw(W)
0
120
50
ns
ALE set-up time after write
Data input set-up time before write
Data input hold time after write
CS1 hold time
tSU(W-ALE)
tSU(D-W)
th(W-D)
80
10
th(CS1)
1000
200
Write recovery time
trec(W)
Read mode
( VDD=5 V ± 0.5 V, RTC-72421;Ta=−10 °C to +70 °C, RTC-72423;Ta=−40 °C to +85 °C )
Item
Symbol
tSU(CS1)
tSU(A-ALE)
th(ALE-A)
tw(ALE)
Condition
Min.
1000
50
Max.
Unit
CS1 set-up time
Address set-up time before ALE
Address hold time after ALE
ALE pulse width
50
80
ALE set-up time before read
ALE set-up time after read
Data output transfer time after read
Data output floating transfer time after read
CS1 hold time
tSU(ALE-R)
tSU(R-ALE)
tPZV(R-Q)
tPVZ(R-Q)
th(CS1)
0
ns
50
CL=150 pF
120
70
0
1000
200
Read recovery time
trec(W)
(1) Write mode
VIH2
VIH2
CS1
tsu(CS1)
th(CS1)
tsu(A-ALE)
th(ALE-A)
VIH1
VIH1
VIL1
A0 to A3
CS0
VIL1
tw(ALE)
VIH1
VIH1
ALE
VIL1
tsu(ALE-W)
VIH1
VIL1
VIL1
tsu(W-ALE)
VIH1
tw(W)
WR
VIL1
th(W-D)
tsu(D-W)
VIH1
VIL1
VIH1
VIL1
D0 to D3
(Input)
(2) Read mode
VIH2
VIH2
CS1
tsu(CS1)
tsu(A-ALE)
th(CS1)
th(ALE-A)
VIH1
VIL1
VIH1
VIL1
A0 to A3
CS0
tw(ALE)
VIH1
VIH1
ALE
RD
VIL1
tsu(ALE-R)
VIH1
VIL1
VIL1
tsu(R-ALE)
VIH1
VIL1
tpvz(R-Q)
VIH1
tpzv(R-Q)
VIH1
VIL1
D0 to D3
(Input)
VIL1
Page - 5
MQ - 162 - 03
RTC - 72421 / 72423
2. When ALE is fixed at V
DD
Write mode
( VDD=5 V ± 0.5 V, RTC-72421;Ta=−10 °C to +70 °C, RTC-72423;Ta=−40 °C to +85 °C )
Item
Symbol
tSU(CS1)
th(CS1)
tSU(A-W)
th(W-A)
tw(W)
Condition
Min.
1000
1000
50
Max.
Unit
CS1 set-up time
CS1 hold time
Address set-up time before write
Address hold time after write
Write pulse width
10
ns
120
80
Data input set-up time before write
Data input hold time after write
Write recovery time
tSU(D-W)
th(W-D)
trec(W)
10
200
Read mode
( VDD=5 V ± 0.5 V, RTC-72421;Ta=−10 °C to +70 °C, RTC-72423;Ta=−40 °C to +85 °C )
Item
Symbol
tSU(CS1)
th(CS1)
tSU(A-R)
th(R-A)
Condition
Min.
1000
1000
50
Max.
Unit
CS1 set-up time
CS1 hold time
Address set-up time before read
Address hold time after read
Data output transfer time after read
Data output floating transfer time after read
Read recovery time
10
ns
tpzv(R-Q)
tpvz(R-Q)
trec(R)
CL=150 pF
120
70
0
200
(1) Write mode
VIH2
VIH2
CS1
tsu(CS1)
th(CS1)
VIH1
VIH1
VIL1
A0 to A3
CS0
VIL1
tsu(A-W)
tw(W)
th(W-A)
VIH1
VIL1
VIH1
WR
VIL1
th(W-D)
tsu(D-W)
VIH1
VIL1
VIH1
VIL1
D0 to D3
(Input)
(2) Read mode
VIH2
VIH2
CS1
tsu(CS1)
th(CS1)
VIH1
VIH1
VIL1
A0 to A3
CS0
VIL1
tsu(A-R)
th(R-A)
VIH1
VIL1
VIH1
RD
VIL1
tpvz(R-Q)
tpzv(R-Q)
VOH
VOL
VOH
VOL
D0 to D3
(Output)
(3) Read/write recovery mode
trec(R/W)
VIH1
VIH1
RD,WR
Page - 6
MQ - 162 - 03
RTC - 72421 / 72423
„ Registers
1. Register table
Address
Register
name
Data
Count
(BCD)
A3
A2
A1
A0
Remarks
(Hex)
D3
D2
D1
D0
0
1
2
3
4
5
6
7
8
9
A
B
C
D
0
0
0
0
0
0
0
0
1
1
1
1
1
1
0
0
0
0
1
1
1
1
0
0
0
0
1
1
0
0
1
1
0
0
1
1
0
0
1
1
0
0
0
1
0
1
0
1
0
1
0
1
0
1
0
1
S1
S10
MI1
MI10
H1
s8
s4
s40
mi4
mi40
h4
s2
s20
mi2
mi20
h2
s1
s10
mi1
mi10
h1
0 to 9
0 to 5
0 to 9
0 to 5
0 to 9
0 to1 or 2
0 to 9
0 to 3
0 to 9
0 to 1
0 to 9
0 to 9
0 to 6
1-second digit register
10-seconds digit register
1-minute digit register
10-minute digit register
1-hour digit register
*
mi8
*
h8
H10
D1
*
PM/AM
d4
h20
d2
h10
d1
10-hours digit register
1-day digit register
d8
D10
MO1
MO10
Y1
*
*
d20
mo2
*
d10
mo1
mo10
y1
10-days digit register
1-month digit register
10-months digit register
1-year digit register
mo8
mo4
*
*
y8
y80
y4
y2
Y10
W
y40
w4
y20
w2
y10
w1
10-years digit register
Day-of-the-week register
Control register D
*
CD
30s ADJ
IRQ FLAG
BUSY
HOLD
ITRPT/
STND
STOP
E
F
1
1
1
1
1
1
0
1
CE
CF
t1
t0
MASK
Control register E
Control register F
TEST
24/12
RESET
2. Notes
The counts at addresses 0 to C are all positive logic. Therefore, a register bit that is 1 appears as a high-level signal on the data bus.
Data representation is BCD.
Do not set an impossible date or time in the RTC. If such a value is set, the effect is unpredictable.
When the power is turned on (before the RTC is initialized), the state of all bits is undefined. Therefore, write to all registers after
power-on, to set initial values. For details of the initialization procedure, see "Using the RTC-72421/RTC-72423".
The TEST bit of control register F is used by EPSON for testing. Operation cannot be guaranteed if 1 is written to this bit, so make
sure that it is set to 0 during power-on initialization.
3. Functions of register bits (overview)
Bit name
Function
Not used. Writing to this bit has no effect; reading it always returns 0.
All written BCD code.
* mark
Seconds to year digit
This is special (base 7) counter that increments each time the day digits are incremented. It counts from 0 to 6. Since the value in the
counter bears no relationship to the day of the week, the user can choose the coding that relates the counter value to the day of the
week. The following is just one example of this relationship.
Day-of-the-week digit
Count
Day
0
1
2
3
4
5
6
Sunday
Monday
Tuesday
Wednesday Thursday
Friday
Saturday
The PM/AM bit is 1 for p.m. times; 0 for a.m. times. This bit is valid only for 12-hour-clock mode (when the 24/12 bit is 0); in 24-hour-
clock mode (when the 24/12 bit is 1), this bit is always 0.
PM/AM
30-seconds ADJ
Writing 1 to this bit executes a 30-seconds correction.
The IRQ FLAG bit is set to 1 when an interrupt request is generated in fixed-period interrupt mode. Writing 0 to this bit clears it. Note
that it is possible to write 1 to this bit, but this will have no effect.
IRQ FLAG
In fixed-period pulse output mode, this bit is at 1 while the pulse output is active(While the STD.P pin output is low), and is
automatically cleared when pulse output ends. Writing 0 to this bit while pulse output is active forcibly cancels the pulse output.
Use the BUSY bit when accessing data in the S1 to W registers. This bit is set to 1 during the incrementation cycle of the S1 to W
registers, and is set to 0 otherwise. When the BUSY bit is 1, access to the S1 to W registers is inhibited.
BUSY
HOLD
Note that the HOLD bit must also be used when accessing the S1 to W registers. The BUSY bit is always 1 when the HOLD bit is 0.
There is no need to check the BUSY bit when accessing the control registers (CD, CE and CF).
When 1 has been written to the HOLD bit, the status of the BUSY bit can be checked. While the HOLD bit is 1, any incrementation of
the digits is held just once. (The incrementation is held only once, even if the HOLD bit remains at 1 for two or more seconds.)
Clear the HOLD bit to 0 by forcing the CS1 pin low.
t1,t0
These bits set the timing for fixed-period pulse output and interrupts (1/64 seconds, 1 second, 1minute or 1 hour).
The ITRPT/STND bit sets fixed-period pulse output mode and fixed-period interrupt mode. Write 1 to this bit to set interrupt(INRPT)
mode; when write 0 to it to set pulse output(STND) mode.
ITRPT/STND
The MASK bit disables fixed-period pulse output and fixed-period interrupts. Write 1 to this bit to mask and inhibit these modes; write
0 to it to enable these modes.
MASK
TEST
The TEST bit is used by EPSON for test purposes. Operation cannot be guaranteed if 1 is written to this bit, so make sure that it is
set to 0 during power-on initialization.
The 24/12 bit switches between 24-hour clock and 12-hour clock. Write 1 to this bit to set 24-hour mode; write 0 to it to set 12-hour
mode. When the 24/12 bit is set, both the timer registers and the timer mode must be reset to match. Note that the h20 bit of the H10
register is always in 12-hour-clock mode.
24/12
The STOP bit sets an inhibition on clock operation in 8192 Hz steps which are divisions of the 1 second signal from the RTC’s
internal 32768 Hz oscillation source. The clock is inhibited when the STOP bit is 1, and released again when it becomes 0. The
internal oscillation circuit continues to operate even when the STOP bit is 1.
STOP
The RESET bit resets the part of the counter that is below one second. Write 1 to this bit to reset; 0 to release the reset.
The RESET bit set to 0 when the CS1 pin goes low.
RESET
Page - 7
MQ - 162 - 03
RTC - 72421 / 72423
4. Setting the fixed-period pulse output mode and fixed-period interrupt mode
Mode
pin
Setting of fixed-period output timing
MASK ITRPT/STND ITRPT/STND
STD.P
Fixed-period pulse output mode
Fixed-period interrupt mode
0
0
0
1
Set to 1 when Set low when
t1 bit
t0 bit
0
0
0
1
1
0
1
1
active
"0"
active
Fixed-period pulse output
inhibited
1
0 or 1
Open-circuit
Output period
1/64 s
1 s
1 min.
1 hour
5. Resetting the fixed-period pulse output mode and fixed-period interrupt mode
Mode
pin
IRQ FLAG
IRQ FLAG
STD.P
Reset immediately after the write
Reset immediately after the write
Fixed-period pulse output mode
MASK=0
write 0
("1" → "0")
("L" → "OPEN")
Automatically returned by the set period Automatically returned by the set period
ITRPT/STND=0
No write
("1" → "0")
Reset immediately after write
("1" → "0")
("L" → "OPEN")
Reset immediately after the write
("L" → "OPEN")
Fixed-period interrupt mode
MASK=0
write 0
ITRPT/STND=1
No write
The interrupt request continues, with no reset. Subsequent interrupt are ignored.
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„ Register description
1. Timing registers
(1) S1 to Y10 registers
These registers are 4-bit, positive logic registers in which the digits of the year, month, day, hour, minute, and second are
continuously written in BCD code.
For example, when(1, 0, 0, 1) has been written to the bits of the S1 register, the current value in the S1 register is 9. As
described previously, data is handled by 4-bit BCD codes. Therefore, the S1 to Y10 registers consist of units registers and
tens registers.
When seconds are read, for example, the values in the S1 and S10 registers are both read out to give the total number of
seconds.
(2) W register
The W register is a counter that increments each time the day digits are incremented. It counts from 0 to 6. Since the value in
the counter bears no relationship to the day of the week, the user can choose the coding that relates the counter value to the
day of the week. The following is just one example of this relationship;
Count
Day
0
1
2
3
4
5
6
Sunday
Monday
Tuesday
Wednesday Thursday
Friday
Saturday
(3) H10 register (PM/AM, h20, h10)
The H10 register contains a combination of the 10-hours digit bits and the PM/AM bit. Therefore, the contents of this register
will depend on whether the 12-hour clock or 24-hour clock is selected. If the 12-hour clock is selected, the user must bear in
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2. CD register (control register D)
(1) HOLD bit (D0)
Use the HOLD bit when accessing the S1 and W registers. For details, see "Read/write of S1 to W registers".
HOLD bit
Function HOLD bit
0
1
The BUSY bit is always 1 (the BUSY status cannot be checked).
The BUSY status can be checked. When the HOLD bits is 1 and the BUSY bit is 0, read and write are enabled.
When the HOLD bit is 1, any incrementation in the count is held within the RTC. The held incrementation is automatically
compensated for when the HOLD bit becomes 0. (Second and subsequent incrementations are ignored.) Therefore, if the
HOLD bit is at 1 for two or more seconds in succession, the time will be slightly slow (delay). Make sure that any access to
the S1 to W registers is completed within one second, then clear the HOLD bit to 0.
The status of the BUSY bit remains as set while the HOLD bit is at 1. If the HOLD bit is not cleared temporarily to 0, the
BUSY bit will not indicate any change within the RTC of the BUSY status. Therefore, when checking the status of the BUSY
bit, write 0 to the HOLD bit each time the BUSY bit is read, to update the status of the BUSY bit.
If the CS1 pin goes low while the HOLD bit is 1, the HOLD bit is automatically cleared to 0.
There is no need to use the HOLD bit when accessing the control registers (CD, CE, and CF).
(2) BUSY bit (D1)
The BUSY bit indicates whether or not the digits from the seconds digit onward are being incremented, and is used when
accessing the S1 to W registers. For details, see "Read/write of S1 to W registers".
There is no need to check the BUSY bit when accessing the control registers (CD, CE, and CF).
BUSY bit
Significance of the BUSY bit
Condition
Remarks
0
1
1
Access enable
HOLD=1
The RTC is not counting
Access disabled
The count has been incremented in the RTC (190 µs Max.)
The count cannot be checked
BUSY is always 1
HOLD=0
The status of the BUSY bit remains as set while the HOLD bit is at 1. If the HOLD bit is not cleared temporarily to 0, the
BUSY bit will not indicate any change within the RTC of the BUSY status. Therefore, when checking the status of the BUSY
bit, write 0 to the HOLD bit each time the BUSY bit is read, to update the status of the BUSY bit.
The BUSY bit is a read-only bit, so any attempt to write 1 or 0 to it is ignored.
(3) IRQ FLAG bit (D2)
The IRQ FLAG bit is an internal status bit that corresponds to the status of the STD.P pin output, to indicate whether or not an
interrupt request has been issued to the CPU. When the STD.P pin output is low, the IRQ FLAG bit is 1; when the STD.P pin
output is open-circuit, the IRQ FLAG bit is 0.
When writing data to the CD register, keep the IRQ FLAG bit at 1, except when deliberately writing 0 to it. Writing 0 to the IRQ
FLAG bit cancels its status if it had become 1 at that instant or just before.
i. Interrupt processing (interrupt status monitor function)
Since the IRQ FLAG bit indicates that an interrupt request has been generated to the CPU, it is in synchronization with
the status of the STD.P pin output. In other words, the status of the STD.P pin output can be monitored by monitoring the
IRQ FLAG bit.
In fixed-period pulse output mode, the relationship between the IRQ FLAG bit and the STD.P pin output is as follows:
STD.P pin output
IRQ FLAG bit
Low
1
Open(for open-drain output)
0
The timing of the IRQ FLAG bit and the STD.P pin output in fixed-period pulse output mode is as follows:
*STD.P pin output
IRQ FLAG bit
0
1
0
Approx.
1.95 ms
7.8125 ms
The output levels of the STD.P pin are low (down) and open circuit (up).
ii. STD.P pin output reset function
The STD.P pin output can be reset after an interrupt is generated by writing 0 to the IRQ FLAG bit.
The relationships of this operation are shown below. Note that writing 1 to this bit is possible, but it has no effect.
IRQ FLAG bit
STD.P pin output
1
0
Low
Open(for open-drain output)
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*STD.P pin output
IRQ FLAG bit
0
1
0
1
Interrupt generation (in synchronization
with count incrementation)
Writing of 0 IRQ FLAG bit.
The output levels of the STD.P pin are low (down) and open circuit (up).
Note: If the STD.P pin output remains low as set, subsequently generated interrupts are ignored. In order to prevent
interrupts from being overlooked, write 0 to the IRQ FLAG bit before the next interrupt is generated, to return the STD.P
pin to high.
iii. Initial setting of IRQ FLAG bit
If the fixed-period interrupt mode is not used, set the IRQ FLAG bit to 1. If the fixed-period interrupt mode is used, set the
IRQ FLAG bit to 0.
(4) 30-second ADJ bit (D3)
The 30-seconds ADJ bit provides a 30-seconds correction (by which term is meant a rounding to the nearest whole minute)
when 1 is written to it. The 30-seconds correction takes a maximum of 76.3 µs to perform, and after the correction the 30-
seconds ADJ bit is automatically returned to 0. This operation also clears the sub-second bits of the internal counter down to
the 1/256-seconds counter. During the 30-seconds correction, access to the counter registers at addresses 0 to C is inhibited,
so monitor the 30-seconds ADJ bit to check that this bit has returned to 0, before starting subsequent processing. If no
access is made to the RTC for 76.3 µs or more after 1 is written to the 30-seconds ADJ bit, there is no need to check the 30-
seconds ADJ bit again.
i. Operation of 30-seconds ADJ bit
Writing 1 to the 30-seconds ADJ bit performs a 30-second correction. This 30-seconds correction changes the seconds
and minutes digits as shown below. If the minutes digits have been incremented, an upward carry is propagated.
Status of seconds digits before correction
Status of seconds digits after correction
00 seconds. No carry to the minutes digits.
0 seconds. Carry to the minutes digits.
Up to 29 seconds
30 to 59 seconds
Example: The correction caused by the 30-seconds ADJ bit sets the time within the RTC to 00:00:00 if it was within the
range of 00:00:00 to 00:00:29, or to 00:01:00 if it was within the range of 00:00:30 to 00:00:59.
ii. Access inhibited after 30-seconds correction
For 76.3 µs after 1 is written to the 30-seconds ADJ bit, the RTC is engaged in internal processing, so read to and write
from the S1 to W registers is inhibited. The 30-seconds ADJ bit is automatically cleared to 0 at the end of the 76.3 µs.
3. CE register (control register E)
(1) MASK bit (D0)
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2.Fixed-period interrupt mode (ITRPT/STND=1)
0
1
0
1
MASK bit
0
1
0
IRQ FLAG bit
*STD. P pin
Nothing is output because
the MASK bit is at 1
Interrupt timing
Reset at the point at which 0 is written to the IRF FLAG bit
No interrupts are generated while the MASK bit is at 1
The output levels of the STD.P pin are low(down) and open circuit(up).
(2) ITRPT/STND bit (D1)
The ITRPT/STND bit specifies fixed-period pulse output mode or fixed-period interrupt mode for the fixed-period operating
mode.
The mode selected by each setting of this bit is as follows:
ITRPT/STND
Operating mode
0
1
Fixed-period pulse output mode
Fixed-period interrupt mode
For details of the timing of fixed-period operation, see the section on the t0 and t1 bits below.
(3) t0 (D2), t1 (D3) bits
These bits select the timing of fixed-period operation in fixed-period pulse output mode or fixed-period interrupt mode. There
is no special counter within the RTC for fixed-period operation; the fixed-period operation is performed at the incrementation
of the time (period) specified by the t0 and t1 bits.
i. Setting t0 and t1
Setting these bits specifies the generation timing for fixed-period pulse output or fixed-period interrupts.
t1
0
0
1
1
t0
0
1
0
1
Period(frequency)
1/64 seconds (64 Hz)
1 second (1 Hz)
Remarks
In fixed-period pulse output mode, the STD.P pin output is low
for 7.8125 ms
(not that half the 1/64 second period is 7.8125 ms)
1 minute (1/60 Hz)
1 hour (1/3600 Hz)
ii. STD.P pin output control
The timing of STD.P pin output is at the incrementation of the period specified by the t0 and t1 bits.
Example : STD.P pin output when 1 hour is set
(Conditions: t0=1, t1=1, MASK=0)
PM 1:00
PM 2:00
Fixed-period pulse output mode
(ITRPT/STND=0)
STD.P pin output
Automatic reset after 7.8125 ms
STD.P pin output
Fixed-period interrupt output mode
(ITRPT/STND=1)
Reset by writing 0 to IRQ FLAG bit
iii. Frequency of STD.P pin output in fixed-period pulse output mode
In fixed-period pulse output mode, the timing of output is determined by the frequency of the internal crystal unit. This
means that the output can be used to measure any error in the frequency of the crystal unit.
Note: The 30-seconds correction could generate a carry. If such a carry occurs when the t0 and t1 bits are set to
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4. CF register (control register F)
(1) RESET bit (D0)
Writing 1 to the RESET bit clears the sub-second bits of the internal counter down to the 1/256-seconds counter. The reset
continues for as long as the RESET bit is 1. End the reset by writing 0 to the RESET bit. If the level of the CS1 pin goes low,
the RESET bit is automatically cleared to 0.
(2) STOP bit (D1)
Writing 1 to the STOP bit stops the clock of the internal counter from the 1/8192 second bit onward. Writing 0 to the STOP bit
restarts the clock.
This function can be used to create a cumulative timer.
(3) 24/12 bit (D2)
Set the 24/12 bit to select either 12-hour clock or 24-hour clock as the timer mode. In 12-hour clock mode, the PM/AM bit is
used.
i. Switching between 12-hour clock and 24-hour clock
Writing 1 to the 24/12 bit selects 24-hour clock mode. In 24-hour clock mode, the PM/AM bit is inoperative and is always
0. Writing 0 to the 24/12 bit selects 12-hour clock mode. In 12-hour clock mode, the PM/AM bit becomes valid. It is 0 for
a.m. times and 1 for p.m. times.
ii. Overwriting the 24/12 bit
Overwriting the contents of the 24/12 bit could destroy the contents of the registers from the H1 register upward (from the
1-hour digit upward). Therefore, before overwriting the 24/12 bit, it is necessary to save the contents of the hour (H1,
H10), day (D1, D10), month (MO1, MO10), year (Y1, Y10), and day-of-the-week (W) registers, then re-write the data back
into the registers to suit the new timer mode, after overwriting the 24/12 bit.
(4) TEST bit (D3)
The TEST bit is used by EPSON for test purposes. Operation cannot be guaranteed if 1 is written to this bit, so make sure
that it is set to 0 during power-on initialization.
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„ Using the RTC-72421/RTC-72423
1. Power-on procedure (initialization)
When power is turned on, the contents of all registers and the output from the STD.P pin are undefined. Therefore, all the registers
must be initialized after power on. Follow the procedure given below for initialization.
Power On
Start the counter
At ths point, there is no need to
(A)
Initialize the control registers
check the BUSY bit.
Check the status of the BUSY bit
(B)
(C)
STOP and RESET the counter
Set the current time in the registers
1
(initialize the S to W registers)
Start the counter and release
the HOLD status
(A)
From here on, check the status of the
BUSY bit before accessing any of the
D
E
F
registers, except for the C , C and C
control register.
To next process
For details of processes (A) to (C), see next page.
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(A)Starting the count
START
Set the CF register
←
Reg.F
0*00B
←
←
←
TEST
24/12
STOP
0
0 or 1
0
0
←
RESET
Set the CE register
This setting is not necessary when
the STD.P pin is not used
Reg.D
← 0*00B
←
←
←
30 s ADJ
IRQ FLAG
HOLD
0
Set the IRQ FLAG bit to 0 when fixed-period
interrupt mode is used, or to 1when it is not
used.
0 or 1
0
To next process
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2. Read/write of S1 to W registers
Use one of the procedures shown below to access registers other than the control registers (CD, CE, and CF) while the RTC is
operating. Note that the control registers can be accessed regardless of the status of the BUSY bit.
Read or write when the HOLD bit is used
From previous process
HOLD bit ← 1
From previous process
HOLD bit
←
1
Read the BUSY bit
Read the BUSY bit
NO
or
NO
BUSY bit = 0?
YES
BUSY bit = 0?
YES
HOLD bit ← 0
HOLD bit ← 0
Read required digit data or
set the time
Read requierd digit data or
set the time
Wait 190 µs
HOLD bit ← 0
HOLD bit ← 0
To next process
To next process
Read when the HOLD bit is not used
From previous process
Read the required digit data
(1st time)
Store the read data (A data)
Read the required digit data
(2nd time)
Store the read data (B←data)
NO
A=B?
YES
To next process
The operation when the HOLD bit is not used involves reading the same digit twice and comparing the read values. This is to
avoid the problem of reading unstable data that would occur if the data was read while the RTC was incrementing the count.
3. Write to 30-second ADJ bit
The 30-seconds ADJ function is enabled by writing 1 to the 30-seconds ADJ bit. Note that the counter registers (S1 to W) cannot
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RTC - 72421 / 72423
4. Using the CS pin
1
The RTC-72421/RTC-72423 has 2 chip-select signal systems: CS0
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RTC - 72421 / 72423
„ Examples of connection to general-purpose microprocessor
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„ External dimensions
1. RTC-72421
23.1 Max.
6.3
7.62
0.2
Min.
4.2
Max.
1.52
0.46
0.25
2.54
Min.
2.54
0 - 15
2. RTC-72423
16.3 Max.
7.9
12.0
0.1
Min.
2.8
Max.
0.2
0.35
1.0
Unless otherwise stated, all units are [mm]
1.27
0 - 10
„ Marking layout
Type
Frequency tlerance
Indications of frequency tolerance
Type
Indication
Tolerances
±10 x10-6
±50 x10-6
±20 x10-6
±50 x10-6
RTC72421
A
A
B
RTC-72421
A
RTC-72423
No indications
EPSON 6053C
Logo mark
Manufacturing lot no.
Note: The illustration is a general representation of the content and location of information on the
label, and is not a detailed specification of the typeface, size or positioning of printing used on the
label.
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RTC - 72421 / 72423
„ Reference data
[Finding the frequency stability]
1. Example of frequency and temperature characteristics
θT = +25 C Typ.
°
1. Frequency and temperature characteristics can be approximated
using the following equations.
10-6
×
= -0.035 10-6 Typ.
α
×
0
∆fT = α ( θT - θX )2
: Frequency deviation in any
temperature
∆fT
-50
-100
-150
( 1 / °C2 )
: Coefficient of secondary temperature
α
( −0.035±0.005 ) × 10-6 / °C2
: Ultimate temperature (+25±5 °C)
: Any temperature
θT
( °C )
θX ( °C )
-50
0
+50
+100
2. To determine overall clock accuracy, add the frequency precision
and voltage characteristics.
Temperature [ C]
°
∆f/f = ∆f/fo + ∆fT + ∆fV
: Clock accuracy (stable frequency) in
any temperature and voltage.
∆f/f
: Frequency precision
∆f/fo
∆fT
: Frequency deviation in any
temperature.
: Frequency deviation in any voltage.
∆fV
3. How to find the date difference
Date Difference = ∆f/f × 86400(s)
* For example: ∆f/f = 11.574 × 10-6 is an error of
approximately 1 second/day.
2. Frequency voltage characteristics ( Typ. )
Frequency[x10-6]
3. Current consumption voltage characteristics ( Typ. )
Current consumption[µA]
Condtions
5 V reference,Ta=+25 °C
Conditions
CS1=0 V, No load, Ta=+25 °C
5
+4
+2
0
4
3
2
1
2
3
4
5
6
DD
Supply Voltage(V ) [V]
-2
-4
2
3
4
5
6
DD
Supply voltage(V
)
Note:
This data shows average values for a sample lot.
For rated values, see the specifications.
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RTC - 72421 / 72423
„ Application notes
1. Notes on handling
This module uses a C-MOS IC to realize low power consumption. Carefully note the following cautions when
handling.
(1) Static electricity
While this module has built-in circuitry designed to protect it against electrostatic discharge, the chip could still be
damaged by a large discharge of static electricity. Containers used for packing and transport should be
constructed of conductive materials. In addition, only soldering irons, measurement circuits, and other such
devices which do not leak high voltage should be used with this module, which should also be grounded when
such devices are being used.
(2) Noise
If a signal with excessive external noise is applied to the power supply or input pins, the device may malfunction or
"latch up." In order to ensure stable operation, connect a filter capacitor (preferably ceramic) of greater that 0.1 µF
as close as possible to the power supply pins ( between VDD and GND ). Also, avoid placing any device that
generates high level of electronic noise near this module.
∗ Do not connect signal lines to the shaded area in the figure shown in Fig.1 and, if possible, embed this area in a
GND land.
(3) Voltage levels of input pins
Apply signal levels that are as close as possible to VDD and ground, to all pins except the CS1 pin. Mid-level
potentials will cause increased current consumption and a reduced noise margin, and can impair the functioning of
the device.
Since it is likely that power consumption will increase excessively and operation cannot be guaranteed, the setting
of the voltage range of VIH2 and VIL2 at the CS1 pin should be such that the system is designed so that it is not
affected by ripple or other noise.
Note that the CS1 pin cannot handle a TTL interface.
(4) Handling of unused pins
Since the input impedance of the signal pins is extremely high, operating the device with these pins open circuit
can lead to malfunctions due to noise. Pull-up or pull-down resistors should be provided for all unused signal pins.
The N.C. pins should be connected to either VDD or GND, to prevent noise. If not using the ALE pin, connect it
directly to VDD.
2. Notes on packaging
(1) Soldering heat resistance
If the temperature within the package exceeds +260 °C, the characteristics of the crystal oscillator will be degraded
and it may be damaged. The reflow conditions within our reflow profile is recommended.
Therefore, always check the mounting temperature and time before mounting this device. Also, check again if the
mounting conditions are later changed.
∗ See Fig. 2 profile for our evaluation of Soldering heat resistance for reference.
(2) Mounting equipment
While this module can be used with general-purpose mounting equipment, the internal crystal oscillator may be
damaged in some circumstances, depending on the equipment and conditions. Therefore, be sure to check this. In
addition, if the mounting conditions are later changed, the same check should be performed again.
(3) Ultrasonic cleaning
Depending on the usage conditions, there is a possibility that the crystal oscillator will be damaged by resonance
during ultrasonic cleaning. Since the conditions under which ultrasonic cleaning is carried out (the type of cleaner,
power level, time, state of the inside of the cleaning vessel, etc.) vary widely, this device is not warranted against
damage during ultrasonic cleaning.
(4) Mounting orientation
This device can be damaged if it is mounted in the wrong orientation. Always confirm the orientation of the device
before mounting.
(5) Leakage between pins
Leakage between pins may occur if the power is turned on while the device has condensation or dirt on it. Make
sure the device is dry and clean before supplying power to it.
Fig. 2 Reference profile for our evaluation of Soldering heat resistance.
Fig. 1: Example GND Pattern
Temperature [ °C ]
RTC-72421
+260 °C Max.
−1 ∼ −5 °C / s
RTC-72423
+1 ∼ +5 °C / s
+170 °C
100 s
+220 °C
35 s
+1 ∼ +5 °C / s
Pre-heating area
Stable Melting area
time [ s ]
Page - 21
MQ - 162 - 03
Application Manual
Distributor
AMERICA
EPSON ELECTRONICS AMERICA, INC.
HEADQUARTER
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Phone: (1)800-228-3964 (Toll free) : (1)408-922-0200 (Main) Fax: (1)408-922-0238
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