Q
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.
A
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.