USART in the 16F628

[Andre Kesteloot]

Larry Kayser wrote:

> Greetings:
>
> I have for some days been struggling with achieving consistent and accurate
> serial port operation, especially when the Interrupts are being hit at a
> high rate.  The APNOTE from MICROCHIP does not work most of the time and
> never worked properly.  However a fine piece of work by Tom McGahee,
> PICUART.ASM for the 16C74A should be adaptable to the 16F628.
>
> It was adaptable and works like a charm.  I have now tried this with the
> following Oscillator configurations.  For the 16F628, the Internal 4 MHz,
> an external 4 MHz crystal, a 1.8432 MHz crystal and with a high speed
> 16F628 it ran just fine with a 21.7 MHz crystal.
>
> I will send any and all who ask a copy of this ASM file, which I happen to
> call PIC8_4B.ASM, configured to run on a 4 MHz crystal or 4 MHz internal
> oscillator by just compiling it with MPASM.
>
> I will decline to express my thoughts about Microchip documentation and
> product support.  It is suffice to say that my first copy of CPM-80, the
> one with both handwritten and typewritten documentation from Gary Kendall
> about 1976/7 was of higher quality and vastly more accurate than what I
> have received from Microchip for the 16F628.
>
> Larry Kayser
> VA3LK