'Found difference between 16F628 and 16F628A'
Rochester, 31 augustus 2005.
Yesterday I received my $12.50 JDM programmer from eBay and now I can finally program the 16F628A (for some reason the El Cheapo can handle the 16F628, but not the 16F628A, regardless of software used). So I happily reassembled my application for the new target, programmed the device and used it. At first all seemed to be working fine, but then I started noticing little glitches.
I was already aware of some differences (the 16F628A consumes less power and uses a different programming method) and I had read in the datasheet that the configuration bits changed, that code protection is no longer partial, that timer 1 and the internal oscillator work differently but this was something else. I debugged for a while, and then I discovered that the 16F628A doesn't allow you to read the EEPROM while it is writing to it. On the 16F628, if you read the EEPROM while writing to it, it returns 0xFF and writes the correct value. On the 16F628A, if you read the EEPROM while writing to it, it returns 0xFF but also stores 0xFF into it, instead of the requested value. This is a rather unfortunate difference, which is why I decided to let you know.
Of course, I tested this only with two 16F628 and two 16F628A that I bought at the same time. It might be that some 16F628 exhibit the same behaviour and that some 16F628A don't. But it really seems like something that has been introduced in the 16F628A.
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