eeprom

[dave.t]

Happy new year to you all!

I am designing a controller using a pic 877 and am going to use some external Fram memory to store the controllers settings.
I am a bit worried that in the event of Brown out when writing to the memory the settings could be corrupted.Is this a possibility and how can I resolve this.

Many thanks for your thoughts.
Regards.
Dave
___________________________
This message was ported from CCS's old forum
Original Post ID: 10506

[PCM programmer]

:=Happy new year to you all!
:=
:=I am designing a controller using a pic 877 and am going to use some external Fram memory to store the controllers settings.
:=I am a bit worried that in the event of Brown out when writing to the memory the settings could be corrupted.Is this a possibility and how can I resolve this.
:=
--------------------------------------------------

I used FRAM on a data logger project. The power came from
a 12v automobile charging system (14.3v when running).
So before I did a write to FRAM, I used the A/D converter
on the PIC to check the input voltage. If it was at least
10 volts, then I did the write to FRAM. I carefully measured
the time required to do the write operation, with a logic
analyzer. I also measured how long the power supply stayed
"up" (at +5v) when the input power was at +10v and then was
shut off. I used two resistors to make a voltage divider,
so I could reduce the input voltage to a safe level for the
PIC's A/D converter. (Remember that the PIC A/D requires
an input impedance of less than 10K -- so choose resistors
according to that rule).

I don't know where your input voltage comes from. If it's
the AC line, then I know there are chips that have a "AC power
fail" detect circuit. If the AC voltage is missing for several
60 Hz (or 50 Hz) cycles, then the chip puts out a warning
signal. I think Maxim Semiconductor makes this chip.
___________________________
This message was ported from CCS's old forum
Original Post ID: 10512

[dave.t]

:=:=Happy new year to you all!
:=:=
:=:=I am designing a controller using a pic 877 and am going to use some external Fram memory to store the controllers settings.
:=:=I am a bit worried that in the event of Brown out when writing to the memory the settings could be corrupted.Is this a possibility and how can I resolve this.
:=:=
:=--------------------------------------------------
:=
:=I used FRAM on a data logger project. The power came from
:=a 12v automobile charging system (14.3v when running).
:=So before I did a write to FRAM, I used the A/D converter
:=on the PIC to check the input voltage. If it was at least
:=10 volts, then I did the write to FRAM. I carefully measured
:=the time required to do the write operation, with a logic
:=analyzer. I also measured how long the power supply stayed
:="up" (at +5v) when the input power was at +10v and then was
:=shut off. I used two resistors to make a voltage divider,
:=so I could reduce the input voltage to a safe level for the
:=PIC's A/D converter. (Remember that the PIC A/D requires
:=an input impedance of less than 10K -- so choose resistors
:=according to that rule).
:=
:=I don't know where your input voltage comes from. If it's
:=the AC line, then I know there are chips that have a "AC power
:=fail" detect circuit. If the AC voltage is missing for several
:=60 Hz (or 50 Hz) cycles, then the chip puts out a warning
:=signal. I think Maxim Semiconductor makes this chip.


Thanks.
I am monitoring the ac line to detect zero crossover points to control a load,so I have a good indication of the state of the mains supply. A case of "I cant see the wood for the tree's" I think!.
Dave.
___________________________
This message was ported from CCS's old forum
Original Post ID: 10530

[Sherpa Doug]

:=Happy new year to you all!
:=
:=I am designing a controller using a pic 877 and am going to use some external Fram memory to store the controllers settings.
:=I am a bit worried that in the event of Brown out when writing to the memory the settings could be corrupted.Is this a possibility and how can I resolve this.
:=
:=Many thanks for your thoughts.
:=Regards.
:=Dave

I have used multiple copies each with a checksum. If power dies while writing a copy that copy will have a bad checksum, but another copy with a good checksum should be fine, though it may be from the time-before-last.

___________________________
This message was ported from CCS's old forum
Original Post ID: 10535

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