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ADUC842 stopped working at 16 MHZ, CHIPID=0xA6?

Question asked by johnbyrd1952 on Mar 8, 2012
Latest reply on Sep 27, 2012 by johnbyrd1952

I have a problem where my aduc842 reports CHIPID=0xA6 instead of 0xA5.  I also cannot set the PLLCON to 0x00 (16MHZ).  The PLLCON returns to 0x13 (2 MHZ).  I can set PLLCONto 8 MHZ 0x01, but it reports 0x11.  The CPU is embedded in epoxy so I can't check the part number to verify that it is the right part, or I can't check the voltage since the regulator is also embedded.  What microcontroller is associated with 0xA6?  Is it possible that the 5 volt regulator is only putting out 3 volts and will not run at 16 MHz?  I'm trying to find a clue as to why I can't get the part to work at 16 MHz.  It was working at one time, so I suspect a register got reset that is causing the problem.

 

Message was edited by: John Byrd I just had 2 other boards with the same problem returned to me from a customer.  I need some help to determine why the PLLCON bit 4 shows up as a 1 instead of 0.  This is a reserved bit which I set to 0, but it returns 1.    Also the CHIPID does not match the 0xA5 for the ADUC842 as described in other discussions.  The CHIPID is 0xA6, which is not referenced in the other discussion.  What part is assigned to 0xA6?  This register is not defined in the datasheet.  All 3 of these boards worked properly before shipping, but will not work at 16MHz now.

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