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Hi All H/W system has: 1) 89C51RD2 (MC) 2) DS1232 as system reset IC ( Resets sys,if its strobe pin in not toggled in 1.2 Sec). In normal execution mode 1 port pin of MC toggles strobe pin of DS1232 before 1.2 Sec expires. ISP feature of 89C51RD2 is to be used for loading hex file in its flash. Since strobe pin is not toggled in ISP mode,DS1232 keeps on resetting system. and hence ISP is not able to load hex file. Sorry to say that this problem is not related to keil. can anybody provide way out of this if any one who have faced this problem. rgds Naresh
1) 89C51RD2 (MC) 2) DS1232 as system reset IC ( Resets sys,if its strobe pin in not toggled in 1.2 Sec). Why on earth are you using an external watchdog for a chip that has two internal puppies. There is the 'real' one which can not be disabled except by reset and the old 'intel kluge' using PCA4. replace your reset chip with a regular supervisor and use the internal puppy. Erik
Hi Erik, I can see where you are coming from in that it does seem 'surplus to requirements' using this simple watchdog chip, but in part we do a similar thing using a more complex watchdog chip that also ensures that spurious read/writes (by blocking the chip select) can't corrupt our battery backed data as the power cycles. But, back to the case in hand, there are two schools of thought (e.g. see http://www.embedded.com/story/OEG20021211S0032 for a more in depth view) both of which have their pros and cons and in the case of an internal watchdog, a program that is out of control may do unpredicatble things like inadvertently disable the internal watchdog timer function and thus never be brought back under control and thus Naresh may feel a lot safer with an external chip that 'he knows and understands' rather than chance using the internal watchdog. So in conclusion, he has two choices either (as has already been said) break the signal to the reset of the processor or (rely on the internal watchdog and) remove the DS1232 chip. Mark. :-)
"a program that is out of control may do unpredicatble things like inadvertently disable the internal watchdog" Also, in many cases internal watchdogs default to being disabled - so if your code has a bad reset and fails to start properly, an internal watchdog may never catch it! Dunno if that applies in this particular case, though.
Erik Mark is correct, there are other reasons above that also: 1)internal watch dog timer in RD2 is providing less time delay hence has to be refreshed frequently.system is performing process which takes on average 1 sec to execute and during this period i do not want watch dog to be refreshed/reset my system. 2)Board has additional chips(other than MC):some require --> /rst and others --> rst. so best was to use external watchdog/reset IC,which will make system reset efficient. -------------------------------------------- regarding reset IC & ISP,best is to use seperate RC reset ckt for MC while it is in ISP mode. Rgds Naresh