| ??? 08/12/07 03:45 Read: times |
#143120 - Some hints Responding to: ???'s previous message |
Richard said:
I am curious, however, why it appears that with slow decay on Vcc, 805x's (and I'm not for a moment suggesting it couldn't happen with absolutely any MCU) the content of external BBRAM frequently seems to become corrupted. This suggests that the MCU is doing something despite the fact that RESET is asserted, as I've seen this in cases where a MAX1232 was installed, as I previously stated. Yes, I understand what you mean and such frequent BBRAM content corruptions would heavily alarm me too! Some hints: 1. Is tPD, tF, tR, tPU and tREC of DS1230Y fullfilled in your application? 2. Also, is tF of MAX1232 fullfilled? 3. As the write protect of DS1230Y becomes invoked, when Vcc falls under 4.25V I would heavily recommend to choose a trip point of 4.62V at MAX1232, which I do in all of my applications. Don't choose 4.37V! If the DS1230Y stops write commands, before the micro becomes reseted, then, of course, you will find BBRAM content "corruptions", or concretely spoken missing write activities. If you are not sure, whether the micro does something wrong with your BBRAM after the MAX1232 outputs a reset signal when Vcc is decaying, you could monitor the !WR or ALE/!Prog line and hunt for unallowed pulses. An edge triggered scope could do this job quite well. Then, after the total decay of Vcc, you could check the BBRAM content and, if a corruption occured without forbidden !WR pulses, then the BBRAM is faulty, but not the micro. Kai |
