More Newbie Questions

william chan

1. Why the Propeller does not come with a separate watchdog clock?

2. Can the transistors 2N3904 and 2N3906 in the recommended Serial PC Comm. circuit be replaced with other common transistors like 2N4401 and 2N4402?

3. Can jitters in the power supply or surges cause the Propeller to overwrite some bytes in its on program on the eeprom?
Will the program be more likely to corrupt if the program frequently writes to the upper part of the 24c512 eeprom frequently due to jitters.

Thanks.

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
www.fd.com.my
www.mercedes.com.my

Mike Green

1) It is very easy to have a "spare" cog act as a watchdog timer and the whole philosophy of the Propeller is based on the idea of multipurpose processors, even when the function is very simple.

2) Probably.· The 2N3904 and 2N3906 are general purpose transistors and any similar NPN / PNP general purpose or switching transistors should work.

3) Theoretically a noisy or "spiky" power source could cause corruption of the EEPROM when writes are going on.· The way to fix this is to filter the power source.· Normally, a marginal supply voltage will cause the Propeller to reset and the EEPROM will not do a write when the supply voltage is marginal.· Writing to the upper 1/2 of a 64K EEPROM should not normally cause problems in the lower 1/2 of the EEPROM, but bad noise on the SDA/SCK lines could theoretically cause the write address to be interpreted wrong if the timing of the pulse is just right.· These lines are normally well protected and frequently will have Schmidt triggers to prevent this sort of thing.