Problem regarding Real time Clock (I2C or SPI)

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Hi Every1

I am doing my project regarding automation of 6 valves using at89c51. there i need to store data of valve flow in computer through rs232.
i want to update this database as file and then it into folders for every 24 hours continuosly. for this time i want to interface RTC to my controller.
So, can anyone suggest me that which RTC will better to use here(SPI or I2C). and also suggest me that what we have to see at the time of choosing RTC.

and what other things needed in this extra to interface RTC with at89c51.

If i go for I2C then is there any clock pulse needed to RTC from microcontroller.
 
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Choose I2C RTC. If you use SPI RTC then you need 4 pins (1 pin to select device). In I2C you need only 2 wires but as you micro doesn't have hardware i2c you have to use software i2c.
 
hai
if your microcontroller has more pins free you can use SPI RTC, as this protocol is easy to impliment than I2C, other wise you can use I2C RTC.
 
according to me use I2C based RTC bzoz less pin counts and RTC doesn't require fast communication bcoz any how it will provide data after 1 second only.
 
Hello!

The advantage of SPI is that it's a lot faster. I2C is usually limited to 100 or 400 kbps.
With SPI, you can have faster access. The advantage of I2C is that you can address more
than 1 device on the same bus. But if you just use one device, the advantage is not that
great, and on top of that I2C is often tricky to tune.

I was used to DS 1390 (Maxim), but now I'm going to try MCP7951 which has many
advantages and which costs 1/3 of the price. And it's pin compatible with DS 1390.

The SPI clock is up to 5 MHz in both cases.

Dora.
 
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