Shop OBEX P1 Docs P2 Docs Learn Events
Question about plug-and-play EEPROM — Parallax Forums

Question about plug-and-play EEPROM

DiablodeMorteDiablodeMorte Posts: 238
edited 2007-03-30 04:33 in BASIC Stamp
Hello everybody,
I have a fairly simple question to ask you all: Is it ok for me to unplug/plug an eeprom into the basic stamp while it is running. Ie, I want to be able to have the Basic Stamp running(And power flowing) and I want to be able to disconnect Eeprom1, and reconnect eeprom2. I then want the basic stamp to read from eeprom2. Is that possible w/o unplugging power, unconnecting eeprom1, connecting eeprom2, and reconnecting power?

Comments

  • allanlane5allanlane5 Posts: 3,815
    edited 2007-03-30 02:00
    That scenario is really outside of how the vendor expected their chip to be used.

    The BS2 is probably robust enough to do that -- IF you set the data and clock pin you'll use to access the eeprom as INPUT.

    The question comes -- how will you pull out the eeprom? If you manage to short ground and Vdd together with the removal tool, this isn't going to work. Most 'hot plug' approaches connect the ground first, then Vdd, then any signal pins. But if any signal pins are set to high-impedance (with the INPUT keyword), it shouldn't be a problem if Vdd or Ground connects first. As long as you don't short the two together with some tool, of course.
  • Mike GreenMike Green Posts: 23,101
    edited 2007-03-30 02:24
    You will eventually damage either the EEPROM or the Stamp or both. At the very least you need to mount the EEPROM on a plug-in card with the ground pin/tab a bit longer than the other pins so the card is grounded first when plugging in and last when being removed. The Vdd line should be filtered with a capacitor on it (like 0.1uF) and there should be resistors in the SDA and SCL lines, maybe 470 ohms. Have a look at the Hydra's expansion card for one example of an external EEPROM card.

    If you must use an IC socket, use a zero-insertion force socket to minimize damage to the pins and have some kind of switch to remove power from the EEPROM socket for removal and insertion. This includes either disconnecting the SDA and SCL lines from the Stamp or somehow instructing the Stamp to ground them (the Stamp could also control the power to the socket).
  • DiablodeMorteDiablodeMorte Posts: 238
    edited 2007-03-30 04:14
    Ok, so, is my idea really not feasible? I really just need a way to be able to plug and play some type of electronic storage for the Basic Stamp.

    Note, the way the eeprom is going to be inserted will be with lots of force but I'm planning on connecting the Eeprom to sometype of PCB w/ tab thingy.
  • Mike GreenMike Green Posts: 23,101
    edited 2007-03-30 04:33
    Like I said, look at how the Hydra Memory Expansion Card is implemented (www.parallax.com/images/prod_jpg/32361.jpg). You only need 4 pins (SCL, SDA, +5V, Gnd) in your case and you could use 0.1" header pins and a matching socket on your board rather than the Hydra's 20 pin socket.
Sign In or Register to comment.