[SOLVED] ds1307 doesnot run when disconnected from vcc

[avirajose]

hi all,
I have sucessfully interfaced ds1307 with pic16f877a and is working fine. But it only starts its oscillation when in vcc only. When i disconnect the vcc ,it stops the oscillation and simply store the previous date.
can anyone suggest me a solutionb for it.

 

[nandhu015]

Post your circuit and code to find out the problem..

 

[rajudp]

check the data sheet there is a bit to enable oscillation i thing it is at address 0 in SEC reg

 

[bigdogguru]

I have sucessfully interfaced ds1307 with pic16f877a and is working fine. But it only starts its oscillation when in vcc only. When i disconnect the vcc ,it stops the oscillation and simply store the previous date.
can anyone suggest me a solutionb for it.

Why would you expect any other result?

The DS1307 requires some method of power to function. It does offer the option to implement a battery backup, which is the purpose of Vbat pin.

The DS1307 has a built-in power-sense circuit that detects power failures and automatically switches to the backup supply. Timekeeping operation continues while the part operates from the backup supply.

Vbat:

Backup Supply Input for Any Standard 3V Lithium Cell or Other Energy Source. Battery voltage must be held between the minimum and maximum limits for proper operation. Diodes in series between the battery and the VBAT pin may prevent proper operation. If a backup supply is not required, VBAT must be grounded. The nominal power-fail trip point (VPF) voltage at which access to the RTC and user RAM is denied is set by the internal circuitry as 1.25 x VBAT nominal. A lithium battery with 48mAh or greater will back up the DS1307 for more than 10 years in the absence of power at +25°C.

BigDog

 

[avirajose]

check the data sheet there is a bit to enable oscillation i thing it is at address 0 in SEC reg

ya, there is a bit to enable oscillation. And it is enabled. But, as i said before,it oscillates while connected to vcc......while disconnected from vcc, it just act as eeeprom just saving the previous time.

 

[prateek_k_chd]

apart from what bigdog has said , do look at the voltage of the battery (if you have hooked up one) . If it is below a particular value ( look up the datasheet) then the ds1307 will stop oscillating and just preserve the last time . This happened with me once - the 3.6v battery i was handed out was actually supplying 1.9v.

 

[avirajose]

k, thanks a lot for all the replies......the problem was with ds1307..Replacing it solved my pro.and is working fine