Rainbow Electronics DS1678 User Manual

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DS1678

Real-Time Event Recorde

FEATURES

§ Real-time clock (RTC)/calendar in binary-

coded decimal (BCD) format counts seconds,
minutes, hours, date, month, day of the week,
and year with leap-year compensation and is
year 2000-compliant

§ Logs up to 1025 consecutive events in read-

only nonvolatile (NV) memory

§ The event trigger is user-programmable and

can be triggered by the falling edge, rising
edge, or rising and falling edges of the

INT pin

§ Event count register provides data on the

number of events that have been logged in the
current event logging mission

§ Programmable real-time clock alarm

§ 32-byte, battery-backed, NV RAM for data

storage

§ Two-wire serial interface allows for a simple

connection to your system

§ Three resolution options are available to trade

off accuracy versus maximum time between
events

§ Underwriters Laboratory (UL) recognized

PIN ASSIGNMENT

1

X1

2

X2

3

V

BAT

GND

4

8-Pin DIP (300-mil)

8-Pin SOIC (208-mil)

Package dimension information can be found at:

http://www.maxim-ic.com/TechSupport/PackInfo.htm

Vcc

8
7

INT

6

SCL

5

SDA

PIN DESCRIPTION

V

BAT

X1 - Crystal Input
X2 - Crystal Output

INT - Interrupt Input/Output

GND - Ground
SDA - 2-wire Input/Output
SCL - 2-wire Clock Input
V

CC

- Battery Supply

- +5V Supply

TYPICAL OPERATING CIRCUIT

ORDERING INFORMATION

DS1678 8-Pin DIP (300-mil)
DS1678S 8-Pin SOIC (208-mil)

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DS1678

DESCRIPTION

The DS1678 Real-Time Clock Event Recorder records the time and date of a non-periodic, asynchronous
event each time the INT pin is activated. The device records the seconds, minutes, hours, date, day of the
week, month, year, and century when the first event occurs. Subsequent events trigger the recording of
the 16-bit elapsed time counter (ETC) into the 2048 bytes of event log memory. This allows for up to
1025 events to be logged.

The event count register contains the total number of events that have been logged in the current event­logging mission. The event count register also allows the user to determine if the data in the event log
memory has rolled over.

Three resolution options allow users to maximize the event log resolution while providing an adequate
maximum time between events without using extra memory locations based on the specific
characteristics of the event being logged. The seconds resolution provides the time of an event down to
the second while allowing up to 18.2 hours between events without using extra memory locations. The
minutes resolution provides the time of an event down to the minute while allowing up to 45.5 days
between events without using extra memory locations. The hours resolution provides the time of an event
down to the hour in which it occurred, while allowing up to 7.5 years between events without using extra
memory locations. Based on the expected frequency of events, the correct setting can be easily selected
to maximize the resolution and memory utilization.

The event can be triggered in three different ways depending on how the user programs the trigger select
(TRx) bits in the control register. The event can be triggered by a falling edge on the INT pin only, a

rising edge only, or it can be triggered by rising and falling edges. Triggering with both the rising and
falling edges allows for monitoring when something is turned on/off and how long it is in either state.

The RTC provides seconds, minutes, hours, day, date, month, and year information with leap-year
compensation, year 2000-compliance, and also provides an alarm interrupt. The 2-wire interface allows
the RTC to function as a stand alone RTC in the system.

The programmable alarm trip points in the RTC will allow a flag to be set in the control register when the
specified time in the alarm trip point register is reached. The flag is readable via the 2-wire interface

during an event logging mission or, when the DS1678 is not in a mission, the

INT pin will become an

output and generate an alarm interrupt if the value in the RTC equals the value in the RTC alarm register
and the duration interval select (DISx) bits are both set to zeros.

The DS1678 operates as a slave device on the 2-wire serial bus. Access is obtained by implementing a
START condition and providing a device identification code followed by a register address. All data is
transferred to and from the DS1678 most significant bit (MSB) first. The address counter will
automatically increment so that subsequent registers can be accessed sequentially until a STOP condition
is executed. When V

falls below 1.25 x V

CC

the device automatically write protects itself, terminates

BAT

any access in progress and resets the device address counter. Inputs to the device via the 2-wire bus will
not be recognized at this time to prevent erroneous data from being written to the device from an out of
tolerance system. When VCC falls below V

the device switches into a low-current battery backup

BAT

mode. Upon power-up, the device switches from battery power to VCC when VCC is greater than

+ 0.2V and recognizes inputs from the system when VCC is greater than 1.25 x V

V

BAT

by releasing

BAT

control of the write protection on the 2-wire bus.

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DS1678

The block diagram in Figure 1 shows the main elements of the RTC event recorder. The device has four
major components: 1) 64-bit RTC and control block, 2) 32-byte user NV RAM, 3) 2048 bytes of event
log memory (1024 events), and 4) 2-wire serial interface.

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DS1678 BLOCK DIAGRAM Figure 1

A

R

2

C

T

A

R

32.768 kHz

DS1678

INT

SCL
SDA

V

C

V

BA

GND

X

OSCILLATOR

ND DIVIDE

CONTROL

LOGIC

2-WIRE SERIAL

INTERFACE

POWER

CONTROL

X1

DDRESS

REGISTE

RTC

USER

RAM

DATA LOG

RAM PORT

DATA LOG
NV SRAM

SIGNAL DESCRIPTIONS

The following paragraphs describe the function of each pin.

VCC – VCC is a +5V input supply. Communication with the DS1678 can take place only when VCC is
connected to a +5V supply.

– Battery input for standard lithium cell or other energy source. All functions of the DS1678 with

V

BAT

the exception of the serial interface circuitry are powered by V
powered by VCC when VCC > V

. If a battery or other energy source is not used, V

BAT

connected directly to ground. UL recognized to ensure against reverse charging current when used in
conjunction with a lithium battery.

See “Conditions of Acceptability” at http://www.maxim-ic.com/TechSupport/QA/ntrl.htm.

GND – Ground.

SCL (2-Wire Serial Clock Input) – The SCL pin is the serial clock input for the 2-wire synchronous

communications channel. The SCL pin is an open drain input, which requires an external pull-up resistor.

SDA (2-Wire Input/Output) – The SDA pin is the data input/output (I/O) signal for the 2-wire
synchronous communications channel. The SDA pin is an open drain I/O, which requires an external
pull-up resistor.

when VCC < V

BAT

. All functions are

BAT

should be

BAT

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DS1678

INT (Interrupt Input/Output) – The INT pin is an I/O that will be activated by an external device to

signify an event has occurred and should be logged. Once the pin is activated, the event will be recorded
in the event log memory and the event counter register will be incremented by one.

The INT pin can be activated in three different ways depending on how the user programs the TRx bits.
The event can be triggered by a falling edge on the INT pin only, a rising edge only, or it can be

triggered by both the rising and falling edges. By logging both the rising and falling edges as events, the
time when something is turned on and turned off can be determined and the amount of time that the
external system was in either state.

This assumes that the external system always starts logging data in a known state. For example, if a light
switch is being monitored and the switch is always in the off position before a mission is started, the first
event would be turning the lights on. The next event would have to be to turn the lights off. The time
between the events would be the amount of time the lights were in the on state. The time from turning the
lights off until the next event, which would be to turn the lights back on again, would be the amount of
time the lights were off.

The INT pin can also be used as an output when the DS1678 is not in an event logging mission. The INT
pin will become an output and generate an alarm interrupt if the DISx bits are both set to zero and the

RTC reaches the preset value in the alarm register. The INT output remains low as long as the status bit
causing the interrupt is present and the DISx bits are both set to zero.

The INT pin is an open-drain input/output with a weak internal pull-down resistor to prevent the pin
from floating if the signal connected to the pin is tri-stated. Without the resistor, the input would float
and potentially log phantom events. With the pull-down resistor, the pin can be transitioned to a low state

causing an event to be recorded if the INT pin was being held high by an outside signal that becomes tri­stated.

X1, X2 – Connections for a standard 32.768kHz quartz crystal, Daiwa part number DT-26S or
equivalent. For greatest accuracy, the DS1678 must be used with a crystal that has a specified load
capacitance of 12.5pF. There is no need for external capacitors or resistors. Note: X1 and X2 are very
high impedance nodes. It is recommended that they and the crystal be guard-ringed with ground and that
high frequency signals be kept away from the crystal area. For more information on crystal selection and
crystal layout considerations, please consult Application Note 58, “Crystal Considerations with Dallas
Real-Time Clocks.”

RECOMMENDED LAYOUT FOR CRYSTAL

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DS1678

CLOCK ACCURACY

The accuracy of the clock is dependent upon the accuracy of the crystal and the accuracy of the match
between the capacitive load of the oscillator circuit and the capacitive load for which the crystal was
trimmed. Additional error will be added by crystal frequency drift caused by temperature shifts.
External circuit noise coupled into the oscillator circuit may result in the clock running fast. See
Application Note 58, “Crystal Considerations with Dallas Real-Time Clocks” for detailed information.

MEMORY

The memory map in Figure 2a shows the general organization of the DS1678. As can be seen in the
figure, the device memory is in one contiguous segment with a data port to access the event log memory.
Since the 2-wire bus only has the capability to use one byte addressing, the DS1678 utilizes the data port
to access the 2048 bytes of event log memory. The address that the next data will be written to is stored
in the address pointer registers LSB (3Fh) and MSB (40h). These will be helpful in recovering all of the
data if a rollover occurs. The address pointer will point to the oldest event in the memory after a rollover.
This is the memory location in event log memory that would be over written by the next event. Read the
data from this point to the end of the memory and the start time stamp, including the 2-byte ETC from
last event. Working backward from the value in the start time stamp, subtract the value in the ETC from
last event to get the time the last event in the memory occurred. Then subtract the values in each of the
2-byte memory locations for elapsed time between events in order to recover the time the previous event
occurred.

The value in the ETC register LSB (3Dh) and MSB (3Eh) is the value in the actual ETC. This is the time
from the last event recorded until logging was stopped. Since a new event has not occurred, this data has
not been stored in the event memory yet.

The data port is made up of three bytes. The first byte (41h) is the event log memory address LSB, the
second byte (42h) is the event log memory address MSB, and the third byte (43h) is the event log
memory data byte. To access data via the data port, the LSB of the event log memory address is written
into 41h, the main memory address pointer will automatically increment to 42h where the event log
memory address MSB data will be written. The next transfer will indicate a read command with a 1 in
the R/

W bit of the 2-wire address byte. The data from the event log memory location corresponding to

the address written into main memory locations 41h and 42h will be available in location 43h to be read.
Any address greater than 43h will read back 00h and will not be able to be written. For address above
43h, the address pointer will increment until it reaches FFh then rollover to 00h.

The event log memory address pointer in main memory locations 41h and 42h will be auto-incremented
to the next higher event log memory address, while the pointer for the main memory will remain at
location 43h. This will allow the event log memory to be read continuously without having to write the
next desired event log memory location prior to each data read. The even address locations in the event
log memory will correspond to the LSB of the elapsed time between events and the odd memory
locations will correspond to the MSB of the elapsed time between events. For more information about
how the data is stored in the event log memory, see Figure 2b.

When the event log memory address pointer gets to the last address location (07FFh), the automatic
incrementing will stop. A new starting address will then have to be written into the event log memory
pointer bytes (41h & 42h) in order to begin reading additional data. The event log memory addresses that
can be put into the pointer (41h & 42h) are 0000h to 07FFh. The five MSB of the address are ignored.

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DS1678

Entering a value greater than 07FFh will result in the address location associated with the value of the
lowest 11 bits of the address.
The RTC and control registers (See Figure 2a for more detail.) are located in the main memory between
addresses 00h and 0Fh. The user NV RAM resides in locations 10h through 2Fh. The event logging
memory data port is located at locations 41h, 42h, and 43h. Memory locations 44h and up are reserved
for future extensions and will read 00h.

The end user can write only to the RTC and control registers and the user NV RAM. The rest of the
memory map is read-only from the end user’s perspective. During an event log mission, all of the
memory is read only. A write will terminate the mission. If there is an event being recorded when the
mission is terminated, the event will finish being recorded before the mission will be stopped and the
values in the MIP and ME bits will not change to 0’s until the mission has completed.

During an event log mission, memory locations 30h and above are not accessible to the user to avoid data
collisions from a user read and an event being logged at the same time. If the user tries to read a location
with an address greater than 2Fh during a mission, the value returned will be 00h.

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DS1678 RTC AND CONTROL PAGE Figure 2a

ADDRESS BIT 7 BIT 6 BIT 5 BIT 4 BIT 3 BIT 2 BIT 1 BIT 0 FUNCTION

00 0 10 SECONDS SECONDS
01 0 10 MINUTES MINUTES
02

03 0 0 0 0 0 DAY OF WEEK
04 0 0 10 DATE DATE
05 0 0 0 10 MO MONTH
06 10 YEAR YEAR
07 10 CENTURY CENTURY
08 MS 10 SECONDS ALARM SECONDS ALARM
09 MM 10 MINUTES ALARM MINUTES ALARM

0A MH 12/24

0B MD 0 0 0 0 DAY-OF-WEEK ALARM
0C
0D

0E ME CLR DIS1 DIS0 RO TR1 TR0 COE Control

0F 0

10
11
12

↓

2F
30 0 10 SECONDS SECONDS
31 0 10 MINUTES MINUTES

32

33 0 0 0 0 0 DAY-OF-WEEK
34 0 0 10 DATE DATE
35 0 0 0 10 MO MONTH
36 10 YEAR YEAR
37 10 CENTURY CENTURY
38 Event 0 Elapsed Time from last Event Counter LSB

39 Event 0 Elapsed Time from last Event Counter MSB
3A Low byte
3B Medium Byte
3C High Byte
3D Low Byte

3E High Byte

3F Low Address Byte

40 High Address Byte

41 Low Address Byte

42 High Address Byte

43 Data Byte

44

↓

FF

0 12/24

MEM

CLR

0 12/24

AM/PM

10 HR

AM/PM

10 HR

MIP CM LOBAT ROF 0 ALMF

AM/PM

10 HR

10 HR

10 HR HOUR ALARM

(reads 00h) Reserved

Byte 1
Byte 2
Byte 3

↓

Byte 32

10 HR

(reads 00h) Reserved

HOUR

RTC

RTC

Alarm

Status

User-

Programmable

NV Memory

HOURS

Time Stamp

And

Elapsed Time

Counter

Event Count

Elapsed Time

Counter (ETC)

Address

Pointer

Data Log

RAM

Port

DS1678

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