External clock for PIC16

[Shipton]

Does the PIC16 - specifically the PIC16F87XA family - need an external clock pulse to operate? If so, how do I generate one of these?

 

[Wilksey]

Looking at the datasheet for that family of uC's, it appears that there is no OSC setting for the internal clock, so I would say it doesn't have an internal clock.

An external clock can be generated in the form of a crystal, nominally at 20MHz, however, if you look at the datasheet you will find under section 14.2, table 14-2 a list of oscillators and the corresponding capacitor values.

I always use a 20MHz with 18-22pf capacitors, depending on the crystal spec, which can be found usually on the suppliers web site. I use RS Components or Farnell for my stuff in the UK. Also, Digikey is a good source. Or a local electronics store.

What you specifiy your clock at is entirely your choice based upon your design, if you have time dependant features or need a high speed baud rate for the serial peripheral, you will need a 20MHz clock, if you are just turning LED's on and off, a 4MHz will do just fine.

Hope this helps.

Wilksey

 

[BeeBop]

Does the PIC16 - specifically the PIC16F87XA family - need an external clock pulse to operate? If so, how do I generate one of these?

The most accurate is to use a crystal and a pair of capacitors to provide a pulse. You can find out more from the data sheet on pages

Get the data sheet from here: top link PIC16F877A
and turn to page 145 - Section 14.2 and you will find everything you need to know about clocking this PIC (and most others..)
The resistor in schematic Figure 14-1, I have never had to use. The value of the caps is not critical, but stay within the limits they suggest and you will be fine.

EDIT: I see I'm a bit slow getting a post up.