pic16f877a + ds1307 dont work

[Guest]

I am working with a pic 16f877a and a ds1307 with a library that you post in this web, my simulation in Proteus is working perfect, but in the protoboard, i have a trouble, doesn't work, could you help me ?

I think that i have the correct crystal, a battery of 3.5 volts in pin 3, pullups resistor of 2K and ...the best try that i make, the time run 20 real seconds were equivalent in the circuit to 8 seconds.

Thats my trouble i shut down and turn on again and it runs 1 second in near to 40 seconds.

i check and check again, like 40000 times and i don t see any mistake, and in this forum in found that the crystal could be the trouble, it says 32.768.

[crystal_lattice]

Your crystal load capacitance could be too big, this will cause it to run slow or not at all, they should be around 7pf if i'm not mistaken.

[elizabeth ann]

in our project we used a TCXO from Maxim which is the DS32kHz. perhaps you are only using an ordinary crystal oscillator which may not be stable at all times. the DS32kHz is temperature-compensated so that the output frequency is very much stable.

try it. good luck!

[jotasmall]

thanks for your help, but i am really surprise, i put a capacitor of 0.1u between vcc and pin2 with the negative side in vcc and it works, but yet doesn´t run in real time.

i suscribe to this forum, because i was reading and i found very useful information...
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my mind is broken!!

[crystal_lattice]

what do you mean by

[cluelesskiller]

Have you read the datasheet for the DS1307, or are you just randomly connecting it from bits and pieces of information you've read on the internet?