RTC Interfacing

8/19/2019 RTC Interfacing

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RTC interfacing


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• Real Time Clock (RTC) is widely useddevice that provides accurate time & datefor many applications. Eg:The !" #$% C

come with such a chip on themother'oard.The RTC chip in the #$% Cprovides time components of hourminute& secondin addition to the datecalander

components of year month & day.The RTCchip uses an internal 'attery which keepsthe time & date even when power is o*.


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+, -!!/ RTC Chip


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0CC

in 1 provides eternal supplyvoltage to the chip

The eternal voltage source is 2 3volt.

4hen 0CC falls 'elow the 5 voltslevel the eternal source is switchedo* and the internal 6i 'atteryprovides power to the RTC


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78+: in - is ground

9+;9+/: The multiple address datapins provides 'oth addresses and datato the chip. 9 simple way of connecting

+,-!!/ to the !3- is shown in the


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+, -!!/ connection to!3-


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• 9, (96E) : 9,( address stro'e) is an ippin.The 9, pin is used for demultipleingthe address & data & is connected to the

96E pin of the !3- chip• %=T: is an ip pin that allows the choice

'etween motorola & intel microcontroller

'us timing.That means when we connect+,-!!/ to the !3- %=T>78+


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• +,: +ata ,tro'e or RE9+ is an ippin.4hen %=+> 78+ for #nteltimingthe +, pin is called the R+signal& is connected to the R+ pin ofthe !3-

• R4: is an ip pin.4hen %=+> 78+

for #ntel timing the R4 pin is calledthe 4R signal& is connected to the4R pin of the !3-


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C,: is an ip pin & active lowsignal.C, only works when theeternal 0cc is connected.4hen 0ccfalls 'elow 1.3v the chip select ipis internally forced to an inactivelevel.This is called write;protected

state. 4hen chip is in write;protectedstate all ips are ignored


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• #R?: #nterrupt Re@uest is an op pin &active low signal.To use #R?the interruptena'le 'its in register$ must 'e set high

• ,?4: ,@uare 4ave is an op pin. Thefre@uency of the s@uare wave is set 'yprogramming register 9

• RE,ET: #8 -! is an reset pin. #t is an inputand is active low pin. #n most applicationsthe reset pin is connected to the 0cc.


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• The +, -!!/ has total of -! 'ytes of R9%space with addresses ;/AB.

• The


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9ddress map


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Turning on the oscillator for the


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Codes to 9ccess the+,-!!/

• 9C966 +E69DmsF RTC needsms after

power;up

%=0 RG-F R>9B register 9address

%=0 9GBF - in +";+1 to turn onoscillator

%=0H IR 9F send it to Register 9 of+,-!!/


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,etting the time

• 4hen we initialiJe time or date weneed to set the +/ of register $ > -.this will prevent any update at the

middle of the initialiJation. aftersetting the time and date we need tomake +/> to make sure that the

clock and time are updated. Theupdate occurs once per second.

• The format of register $ ;


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Th f ll i d i iti li th l k t -" 3! 33 i th $C+


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• The following code initialiJe the clock at -":3!:33 using the $C+mode and the 1 hour clock mode with day light saving time


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,etting the date• 4hen we initialiJe time or date we need to set +/ of register $ to -

=cto'er -th 1

RTC Interfacing

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