I have a new experience in my attempts to adapt the programs, that ran fine on S8252 and S53, but have problems with S8253.

When I came to the final phase, to turn the WDT on, it was another disappointment ! The previous SW actions in the programs do not manage to prevent WDT resets. First I beleived that it could be a small timing difference (the old ones have internal oscillator for that, while the new one uses the processor clock). But according to the datasheet, the difference should be minimal, and also to my advantage, because the times are given for 12 MHz and it runs on 11.0592. Of course, the easiest solution is to select the first higher prescaler value, which is chosen by 3 highest bits in WDTCON (I was in the middle of the range, with 011). No effect ! Next higher - no effect ! The highest, 111 - no effect !

Then I took a simpler of my programs and managed, by few additional ORL WDTCON,#10B, to get it work. But the part where it communicates with user by RS232 didn't yet function. When it writes a string, it stops after 18 characters. And now the most surprising: it stops at the same length at all settings, from 000 to 111 ! Bear in mind that 111 should give more than 2 seconds of WDT time ! Also, the rest of the program, that runs correctly, wasn't affected by any lower setting.

In my opinion, this is a clear evidence that the processor doesn't take the 3 bit setting at all, and that the WDT time is fixed for any setting !

Any experiences on this subject ?


Regards, Slobodan