Migrate from 16F628 to 16F628A

[Melanie]

There is no significant difference between a 628 and a 628A. Code for one will run without changes on the other.

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. If the world was flat, then you were sailing on the edge. Take a random sample of PICs, and some will have their Internal Oscillators spot on, and others will be off significantly to corrupt asynchronous data. Fit a Resonator or Xtal, switch to XT or HS Osc, and your troubles will disappear. Either that, or go buy a really big selection of PICs and outsort the ones that work...

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.

[cooksydesign]

I will attach an external resonator on the 628A in a few hours.

With all the programs I have writen using SerOut, I have never experienced this.

I'll let you know how it goes.

Many thanks.

Brad

[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