I took a look at the errata sheet for the 18f2520 and none of the uart
bugs seemed to be killers for most users. They seem to relate to nine
bit mode, synchronous mode and autobauding. For the average user with
a set baud rate and eight bit transmission I can't see much of a
problem. What am I missing?

Here's what seem to be the relevant bits from:

PIC18F2420/2520/4420/4520 Rev. A1 Silicon Errata Sheet
http://ww1.microchip.com/downloads/en/DeviceDoc/80209d.pdf


18. Module: EUSART

When performing back-to-back transmission in 9-bit mode (TX9D bit in
the TXSTA register is set), an ongoing transmission's timing can be
corrupted if the TX9D bit (for the next transmission) is not written
immediately following the setting of TXIF. This is because any write
to the TXSTA register results in a reset of the baud rate timer which
will effect any ongoing transmission.

Work around
Load TX9D just after TXIF is set, either by polling TXIF or by writing
TX9D at the beginning of the Interrupt Service Routine, or only write
to TX9D when a transmission is not in progress (TRMT = 1).


19. Module: EUSART

When performing back-to-back transmission in 9-bit mode (TX9D bit in
the TXSTA register is set), the second byte may be corrupted if it is
written into TXREG immediately after the TMRT bit is set.

Work around
Execute a software delay, at least one-half the transmission's bit
time, after TMRT is set and prior to writing subsequent bytes into
TXREG.


24. Module: EUSART

The EUSART auto-baud feature may periodically measure the incoming
baud rate incorrectly. The rate of incorrect baud rate measurements
will depend on the frequency of the incoming synchronization byte and
the system clock frequency.

Work around
None.


25. Module: EUSART

In Synchronous mode (SYNC = 1) with clock polarity high (SCKP = 1),
the EUSART transmits a shorter than expected clock on the CK pin for
bit 0.

Work around
None.


26. Module: EUSART

In Synchronous mode, EUSART baud rates using SPBRG values of '0' and
'1' may not function correctly.

Work around
Use another baud rate configuration to generate the desired baud rate.

Cheers,
Zik

On 12/04/06, Olin Lathrop <olin_piclist@embedinc.com> wrote:
> Wouter van Ooijen wrote:
> >> So for a concrete recommendation, get a small handful of
> >> 18F252-I/SP and learn to use them well.
> >
> > Any reason not to start with 18F2520?
>
> Yes, the UART bug.
>
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