Help: 8-Bit O/P from Real-Time Clock Chip

[Darrin]

To those in the know:
I am after designing a Real-Time Clock circuit with 8 Data output lines,
such that at a specific time of the day it should output a set pattern of
data on its output, hold this data at the outputs for exactly 3 hours, then
revert to default (defined) for the rest of the day. Further, this change
should only happen during weekdays and not weekends or public holidays. I am
hoping to achieve this by using a RTC chip. I am presently looking at a
chip which I believe may be able to do this (RTC-62421). Has anyone used
this chip before or have any information like datasheet, specs etc...? Any
ideas or suggestions appreciated - Tks/Darrin

 

[Tilmann Reh]

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I am after designing a Real-Time Clock circuit with 8 Data output lines,
such that at a specific time of the day it should output a set pattern of
data on its output, hold this data at the outputs for exactly 3 hours, then
revert to default (defined) for the rest of the day. Further, this change
should only happen during weekdays and not weekends or public holidays. I am
hoping to achieve this by using a RTC chip. I am presently looking at a
chip which I believe may be able to do this (RTC-62421). Has anyone used
this chip before or have any information like datasheet, specs etc...? Any
ideas or suggestions appreciated - Tks/Darrin

An RTC won't help you anything to solve your problem.
All common RTCs, including the mentioned one, provide data to
be read out of internal registers by some processor interface
(often I2C or SPI, 4-bit bus for the 62421/72421).
None of them provides parallel static data, and none of them
can be configured for particular output signals at given
conditions. Also none of them can be used as stand alone
clocks, they all need a controller for initialisation and
data readout.

What you need is a microcontroller that keeps track of the
weekday (not necessarily the complete date) and time and
generates the appropriate output signal(s).
You might *add* an RTC to avoid losing the time during power
fails.

 

[scada]

To those in the know:
I am after designing a Real-Time Clock circuit with 8 Data output lines,
such that at a specific time of the day it should output a set pattern of
data on its output, hold this data at the outputs for exactly 3 hours, then
revert to default (defined) for the rest of the day. Further, this change
should only happen during weekdays and not weekends or public holidays. I am
hoping to achieve this by using a RTC chip. I am presently looking at a
chip which I believe may be able to do this (RTC-62421). Has anyone used
this chip before or have any information like datasheet, specs etc...? Any
ideas or suggestions appreciated - Tks/Darrin

This is a good job for a PIC chip. www.microchip.com has many application
notes that can guide you. You can program in your RTC as well as controller
functions, and whatever else you need.

 

[dont know]

F'up set to sci.electronics.design.

Please don't x'post without setting a F'up.


An RTC won't help you anything to solve your problem.
All common RTCs, including the mentioned one, provide data to
be read out of internal registers by some processor interface
(often I2C or SPI, 4-bit bus for the 62421/72421).
None of them provides parallel static data, and none of them
can be configured for particular output signals at given
conditions. Also none of them can be used as stand alone
clocks, they all need a controller for initialisation and
data readout.

What you need is a microcontroller that keeps track of the
weekday (not necessarily the complete date) and time and
generates the appropriate output signal(s).
You might add an RTC to avoid losing the time during power
fails.

and to implement that scheme you can use a DS2252T micro (Dallas-
Maxim).

 

[John Fields]

To those in the know:
I am after designing a Real-Time Clock circuit with 8 Data output lines,
such that at a specific time of the day it should output a set pattern of
data on its output, hold this data at the outputs for exactly 3 hours, then
revert to default (defined) for the rest of the day. Further, this change
should only happen during weekdays and not weekends or public holidays. I am
hoping to achieve this by using a RTC chip. I am presently looking at a
chip which I believe may be able to do this (RTC-62421). Has anyone used
this chip before or have any information like datasheet, specs etc...? Any
ideas or suggestions appreciated.

---
I've used a Dallas/Maxim DS1307

http://pdfserv.maxim-ic.com/en/ds/DS1307.pdf

for a similar application, and used its internal 56 X 8 non-volatile
(battery backed-up) memory to hold the data. It communicates over a
two-wire bidirectional bus, so you'll need a µC of some flavor to talk
to it. One nice thing about it, IIRC, is that with a 7.5mAH lithium
battery for backup it'll keep time _and_ retain the data written into
its RAM for over 10 years.

 

[David L. Jones]

To those in the know:
I am after designing a Real-Time Clock circuit with 8 Data output lines,
such that at a specific time of the day it should output a set pattern of
data on its output, hold this data at the outputs for exactly 3 hours, then
revert to default (defined) for the rest of the day. Further, this change
should only happen during weekdays and not weekends or public holidays. I am
hoping to achieve this by using a RTC chip. I am presently looking at a
chip which I believe may be able to do this (RTC-62421). Has anyone used
this chip before or have any information like datasheet, specs etc...? Any
ideas or suggestions appreciated - Tks/Darrin

Hi Darrin,
You are best off using a more common RTC like the DS1307 for which
there are plenty of drivers available for various microcontrollers.
You shouldn't have to write your own just to talk to a simple RTC
chip.
A simple RTC with a small 8 bit microcontroller will do exactly what
you want.
If you want it to be standalone then you'll need some sort of display
like an LCD to set the time/date and alarm times etc. Or else hook it
up to your PC via serial port and do it that way. The EEPROM in the
micro can be used to store the alarm times and other data, and a
battery will keep your RTC going, so the entire design will be
tolerant of power loss.

Regards
Dave

 

[Joerg]

There is also the MSP430 series from TI. These can keep their realtime clock
crystal running while consuming only a few uA. That solution would not need a
separate RTC chip, saving cost and circuit board space.

Regards, Joerg

 

[Michael]

---
I've used a Dallas/Maxim DS1307

http://pdfserv.maxim-ic.com/en/ds/DS1307.pdf

for a similar application, and used its internal 56 X 8 non-volatile
(battery backed-up) memory to hold the data. It communicates over a
two-wire bidirectional bus, so you'll need a µC of some flavor to talk
to it. One nice thing about it, IIRC, is that with a 7.5mAH lithium
battery for backup it'll keep time _and_ retain the data written into
its RAM for over 10 years.

DS1305 is one I use.