ADuC848: Contents of RAM is not fully saved to EEPROM

Document created by analog-archivist Employee on Feb 23, 2016
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My customer  has some technical problems/questions about ADuC848.

They used ADuC836 earlier but now trying to use ADuC848BS62-5. They save
content of the RAM (60 byte/ 15 page) at the EEPROM data memory when power
down. They
did not have any problem with ADuC836 but they can save only 20 byte / 5 page
using ADuC848. And, they need our help to solve the problem.

Please find some working informations below.

Supply voltage (DVdd, AVdd) : 5 Volts
Capacitor connected to power supply : 470 micro Farads
Only ADuC848 draws required currents, the others no.
PLLCON = 00000001B ( Core Clock = 6.29 MHz )
PSMCON = 11000001B ( DVdd, AVdd trip point = 4,63V )

FLASH/EE Data-Memory erased when power-on.

Only write operation done When PSM-INTERRUPT accepted.

 

When the system supply is removed, the Power Supply Monitor (set to 4.63V)
triggers an interrupt which starts the subroutine to save the RAM values to
EEPROM data memory.

The difference between the ADuC848 and the ADuC836 in this regard is that the
ADuC848 comes in two voltage grades, 3V and 5V indicated by the -3 ro -5 at the
end of the part number.

The 5V part, which you are using, has a hardware power-on reset circuit whose
threshold is fixed at 4.63V.

Since the highest threshold for the power supply monitor is also 4.63V, the
Power supply Monitor function cannot be used with the 5V version of the ADuC848
- see page 68 of the ADuC848 datasheet. In fact the part will receive a
hardware reset at around the same voltage as the Power supply monitor is
triggered so there will be little or no time for any last minute processing to
take place.

A common solution, to receive advanced warning of a power down event, is to
obtain the interrupt signal from BEFORE the voltage regulator. Devices like our
ADM708 obtain a power fail signal from before the regulator and therefore give
you some extra time to store the RAM values into EEPROM.

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