Migrate from 16F628 to 16F628A

[Jerson]

There is no significant difference between a 628 and a 628A.However, any form of timing critical functions (such as SEROUT, SERIN etc) on INTERNAL OSCILLATOR is suspect. Just because it worked on a 628 (non-A) means you were lucky. I used to say, never go above 300 Baud on Internal Oscillator, but I've had batches of chips where even that wasn't reliable.

Melanie

I do not quite understand your statements. I use the 628A on a regular basis with 9600 baud for SERIN2 and SEROUT2 with no problems till now. Can you please clarify if this is something to watch out for as a gotcha ??

Jerson

[Melanie]

But are you using it with the PIC set to INTERNAL OSCILLATOR?

[Jerson]

Melanie

Yes, I always use the internal osc. No problems yet.

Jerson

[Melanie]

Then you have been very lucky so far.

The Internal Oscillator is rarely on-frequency, it drifts with temperature and has the stability of a political manifesto at election time. The higher the baud rate, the greater the error margin. If you send or receive a short burst, the few bytes might be within spec, but thereafter you will drift out of specification and communication will be corrupted.

The rule is always to use a Resonator or Xtal when doing timing critical functions.

[Jerson]

Hi Melanie

Well, lucky perhaps. But, the most times, I have used the Serout / Serin functions as a handshake and they carry very little traffic. My products usually power off to a sleeping state which is around 90-95% of their working time. So, perhaps this is where I am lucky.

I can see your point about the internal oscillator drifting with time and temperature; and will keep it at the back of my mind for projects involving longer running times for serial communications.

Hey, btw : I like your analogy about the election manifesto. Looks like none of 'em politicians have reached me yet

Cheers
Jerson

[cooksydesign]

Well, that worked. Thanks. I have to attach resonators to SSOP packages. Quite a few of them.

One more question, please;
The package type is a 16LF628A. Data sheet says it will operate at 2.5 volts. What do I need to do to get it to run on the low voltage? I have a 3 volt regulator in the circuit, and it does not run. At all. Even blinking a LED.

Thanks again.

B

[Ingvar]

Make sure brownout reset in not enabled.