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24LC1025 pin 3 not doing what data sheet says — Parallax Forums

24LC1025 pin 3 not doing what data sheet says

jstjohnzjstjohnz Posts: 91
edited 2014-03-19 10:34 in Propeller 1
I have been using the Atmel AT24C1024, and more recently the On Semi equivalent, in an 8-dip package. Atmel stopped making that part, and the On Semi parts are difficult to get right now, so I started looking at this Microchip part.

Per the data sheet, pin 3 must be held high for the chip to operate (unique to the 1024k part I believe). This is the opposite of the Atmel and On Semi parts where pin 3 must be low. On the first sample that I tested of the Microchip part, it works just fine whether pin 3 is high or low. Just curious if the data sheet is in error or what?

Comments

  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    edited 2014-03-17 16:07
    The datasheet just says that operation will be "undefined" if the A2 pin is grounded or left floating. That could mean almost anything, including correct operation for one chip and not for another.

    -Phil
  • jstjohnzjstjohnz Posts: 91
    edited 2014-03-17 23:39
    Thank you for that, sounds like you may have something more current than I do. The data sheet I'm looking at, dated 2010, says re pin 3: "Non-Configurable Chip Select. This pin must be hardwired to logical 1 state (VCC). Device will not operate with this pin left floating or held to logical 0 (VSS)."

    My older boards have pin 3 tied to ground to accommodate the Atmel and On Semi parts. The newer ones are jumper selectable for Ground or Vcc. If the microchip parts do work with pin 3 grounded then I may be able to use them on the older boards if I run out of the On Semi parts before I run out of the old-style boards.

    So all I need is a simple routine to determine the chip type based on what address the upper 32K responds to, and I should be good to go.
  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    edited 2014-03-18 10:13
    If a data sheet says operation is undefined under a certain condition, I would NEVER operate under that condition, regardless of what an otherwise successful experience might suggest.

    -Phil
  • ericballericball Posts: 774
    edited 2014-03-19 05:16
    Always check for the latest data sheet & errata. Years ago I wired up a board using a preliminary data sheet for a digital filter chip. Unfortunately on the final chip they had changed the pin layout - including swapping some power & ground pins! While it didn't smoke, it got dang hot before it died.
  • LoopyBytelooseLoopyByteloose Posts: 12,537
    edited 2014-03-19 10:34
    Go with Phil's advice -- undefined generally indicates 'we don't know what you will get'.

    And if a product is being discontinued by several manufacturers, there are two likely situations.

    a. No demand for the chip in the broader market
    b. It never worked right to begin with.

    The problem is that manfacturers are reluctant to admit to item b. Early AVR chips were buggy, the makers just marched onward to newer devices.
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