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"NVRAM" for a BS2P40? — Parallax Forums

"NVRAM" for a BS2P40?

Got an interesting project in the form of an old automatic antenna tuner and its apparently defunct microcontroller, an NEC uPD7507C. This has onboard factory-programmed ROM and apparently no way to read its contents, so a redesign in in order. What the OEM circuit does is to control several discrete components to find the best match for a transmitter into a given load, then stores the settings in some internal RAM which is battery-backed. You can turn the device off and let it sit and the settings are retained. Should a better match ever be found (done automatically or commanded manually) the new settings are stored.

Given the large number of I/O pins on the original chip - most of which drive things like indicators, relays and whatnot - my thought is to redesign the entire CPU board to use a BS2P40. This presents a conundrum, there's apparently no way to back up the device's RAM between power-offs. (I'd thought about tying a 9v battery to the Reg pin through a diode, connecting the 5v In pin to the tuner's regulated 5v source and monitoring it to put the Stamp to sleep in the event of power-down).

On to the EEPROM: The stored settings mentioned earlier take a maximum of 80 bytes (probably less) and are only updated when the tuner's internal logic dictates a re-match operation should be performed -or- if the operator commands a manual adjustment. Assuming a few such operations per day max, is the longevity of the Stamp's EEPROM any cause for concern? Or is there a better way to do this?

I have a clean slate to work with in terms of programming and some hardware design, so comments or guidance are welcomed.



  • kwinnkwinn Posts: 8,689
    The closest data sheet I could find for "24WC128J" is attached. That eeprom is rated for 100,000 program/erase cycles, so it should be good for a few decades. An alternative would be to use one of the RTC/NVRAM chips that are designed to run off a battery for several years.
  • JonnyMacJonnyMac Posts: 7,554
    edited 2021-01-16 01:38
    The P1 would give you more horsepower and already has an EEPROM attached. You can overwrite your variables in the EEPROM such that on the next boot that are automatically initialized to the last value -- I have done this many times. You might consider using a FLiP module instead of a BS2P40 -- they're about the same size, but the P1-powered FLiP gives you a lot of advantages (including a significantly lower cost).
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