[SOLVED] basic question Regarding PIC16f887 controller

[jay_3189]

I am using pic16f887 controller and which has two VDD(5V) pin. and I am applying 5v to only one pin by power supply. then is it necessary to short that both pin to use for 5V to take output from controller?
or its no need to short both pin and we can use 5V output from any pin by applying input at only one pin.

and other thing is there is internal crystal oscillator then how to configure it by c programming?

I am new to pic.

 

[Raj Gunaseelan]

Hi Jay,
Just check the two pins for continuity with a multimeter. If they are already connected internally, you may power only one pin. (I've seen 2 VSS pins already connected internally in 28 pin devices).

BTW the internal oscillator is not crystal, its RC oscillator. To clock from the internal oscillator, check the "Section 27. Device Configuration Bits" document from Microchip.


Regards,
Raj Gunaseelan

 

[jay_3189]

Hi Jay,
Just check the two pins for continuity with a multimeter. If they are already connected internally, you may power only one pin. (I've seen 2 VSS pins already connected internally in 28 pin devices).

BTW the internal oscillator is not crystal, its RC oscillator. To clock from the internal oscillator, check the "Section 27. Device Configuration Bits" document from Microchip.


Regards,
Raj Gunaseelan

no I have already check with multimeter. it's not connected. so, I have to short it right?

 

[Raj Gunaseelan]

Yes, you have to.


Regards,
Raj Gunaseelan

 

[jay_3189]

one more question that I am using LM35 temp. ic with pic16f887 ..
is that needed to connect op amp ic in between that?
and if is needed then is that have other any option?

 

[wp100]

one more question that I am using LM35 temp. ic with pic16f887 ..
is that needed to connect op amp ic in between that?
and if is needed then is that have other any option?

Hi,

Provided your 887 is running at +5v then you can feed the lm35 direct to an analogue input.

If you are using a long lead for the lm35 then follow the instructions in its datasheet

 

[Raj Gunaseelan]

Using a voltage follower is better to avoid the microcontroller's internal circuit(pin capacitance, etc) from affecting the signal.


Regards,
Raj Gunaseelan

 

[jay_3189]

Using a voltage follower is better to avoid the microcontroller's internal circuit(pin capacitance, etc) from affecting the signal.


Regards,
Raj Gunaseelan

can you please provide me the diagram for lm35 sensor with voltage follower.

 

[Raj Gunaseelan]

The Connection showing "OPAMP pins 5 & 2" can be neglected.

Regards,
Raj Gunaseelan

 

[jay_3189]

Hi Jay,
BTW the internal oscillator is not crystal, its RC oscillator. To clock from the internal oscillator, check the "Section 27. Device Configuration Bits" document from Microchip.


Regards,
Raj Gunaseelan

thanks for this. but still I have simple doubt that I am using RTC I2C RS232 and ICSP with my controller and I am thinking to use internal oscillator. so, is that ok with that?

 

[Raj Gunaseelan]

thanks for this. but still I have simple doubt that I am using RTC I2C RS232 and ICSP with my controller and I am thinking to use internal oscillator. so, is that ok with that?

Let us see. Internal oscillators are known for their temperature dependency since there is a 'R' factor. This means that the oscillator frequency may vary depending on the IC temperature. This should not be a problem for I2C or SPI, but for RS232 where the baud rates are standardised, change in clock frequency introduces an error in the baud rate. The same is true for the timers and other peripheral clocks(ADC, PWM, etc) as well. If you can afford 3 more components(1 crystal & 2 capacitors) and if the PCB layout allows you, I would suggest to go for an external crystal oscillator.


Regards,
Raj Gunaseelan