Re: Maximum speed, all ports as I/O

John Speth wrote:
At the moment I'm using the following with my PIC16F684:

__CONFIG(FCMDIS & IESODIS & BORDIS & UNPROTECT & MCLRDIS & PWRTEN &
WDTDIS & INTIO);

With this setting, the CPU clock is running at 4 MHz. I've heard tho
that it can run at 16 MHz. (I'm not using an external clock).

Does anyone know what I've to do to get it running at its top speed,
and with all pins set to I/O?

Look at fig 3-1 of the datahsheet. You'll see the internal HF osc is 8 MHz. You can't get it any higher than that without an external clock source.

Correct.

So if the CPU clock is one half of the in HF osc, then you'll need a 32 MHz external clock or crystal to achieve a CPU clock of 16 MHz.

The internal clock runs at the HF rate, but the instruction cycle is 4 clock cycles on a PIC. Bottom line is 2 M ins cycles/sec with internal 8 MHz clock, 5 M ins cycles/sec with external 20 MHz (max datasheet frequency).

You'll also need to become comfortable with reading the data sheets. You won't be able to do much with the device if you can't read the data sheet.

Amen. I find Microchip to have some of the better data sheets.

--
Thad
.

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