Hi Dave,

> Has anyone tried to use the 12c509 at 9600 Baud ? (4Mhz OTP's)
> It works well at 2400 Baud, but even when using the on-chip calibration
> value not all chips work at 9600. I'm guessing that the timing must be
> off enough not to lock. The 509 is being fed from a PC via a RS-232 > TTL
> converter. When I use the JW chip, all is OK. I've run the simulator with
> stopwatch and I get the exact bit delays required. I get the feeling that
> 9600 Baud with these chips is never going to be reliable using the 4Mhz
> internal oscillator. Any ideas or comments would be appreciated.  :-)

A few additional comments.

As mentioned 5% errors should be acceptable for 10 bit (1 + 8 + 1) asynch
data.

The worst case trimming of a 12C50x over temperature and voltage
will be in the 5% region.

The finest trimming step is about 1%

As mentioned the percentage error for the 2400 and 9600 will be the
same so you the error is likely NOT to be the problem in your case.

To achieve the 5% error margins you HAVE to sample close to the mid
bit position so that the sampling point can drift either earlier or
later by the largest margin over the length of the word depending on
the relative bit rates.

There is still some doubt in my mind that the callibration constant
gets loaded properly into the OSCcal register with just one mov
to the register, it is likely just to be me but I load it in 4 times
and have no problem, if I change code to load it just once it sometimes
does not work.  Yuo can have a look at my test code sample at the
link below to see how I do it.  This may be an artifact of using
development programmers for development work but I'm not sure.  I will
worry about it some more when I need those 3 words of code space.

I have shipped products that do either 2400 or 9600 (pin selectable)
on a 12C508 that seem to work ok.  I have plans for others and don't
expect problems.

Cheers
--
Kalle Pihlajasaari   kalle@ip.co.za   http://www.ip.co.za/ip
Interface Products   P O Box 15775, DOORNFONTEIN, 2028, South Africa
+ 27 (11) 402-7750   Fax: 402-7751    http://www.ip.co.za/people/kalle

DonTronics, Silicon Studio and Wirz Electronics uP Product Dealer