Crystal problems!

[umka]

Is it possible to run PIC's without an external crystal?

For some reason I thought it was possible but don't seem to be able to get it to work.

Micro is a 16F628a so pins 15/16 can be connected to external crystal but don't want them to be.

[Ttelmah]

Basic answer. It depends on the PIC. Some have an internal complete oscillator, others _require_ external components.

In your case, the 16F628A, supports this.
Just select the oscillator fuse, as 'INTRC_IO'. Make sure no other oscillator fuse is selected.
Set your 'clock' statement, to use 4000000.

The compiler will then set this up for you.

Only two speeds are available fo the internal oscillator on this chip. 4MHz, or 48KHz. Unless you want super low power, and very low speed, 4Mhz, is your only option.

The extra pins are A6, and A7.

Best Wishes