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Additional EEPROMs — Parallax Forums

Additional EEPROMs

sunblocksunblock Posts: 55
edited 2012-10-31 12:04 in Propeller 1
Being a nosy newbie, I was reading some of the posts and comparing to documentation.The diagram on page 17 of the Propeller Reference Manual v1.2 shows a 24LC256 EEPROM attached to the SCL and SDA--and Propeller. 3.3v in, ground etc. Pretty straight forward stuff for me at this point. The question came to me when reading about the subject of adding additional EEPROMS. the SCL and SDA "busses" terminate in the drawing on pg 17. I have seen other drawings where the SCL and SDA are open ended. In the case of the reference manual, what must be done to "insert" a second (or even 3rd) EEPROM. If the SCL and SDA are open ended, do you just sort of "plug" in each new EEPROM, changing the A0-A2 binaries to designate addresses? What do you do about the 3.3v power that each one needs do they all draw from the 3.3V supplied to the first EEPROM? Probably should be more than one thread I guess.

VR/Sunblock

Comments

  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    edited 2012-10-30 23:07
    Just power each new EEPROM from the same 3.3V supply, and add a 0.1uF bypass cap at the Vdd/Gnd terminals of each one. SCL and SDA can be shared, so long as each EEPROM's A0-A2 pins are strapped differently. Only one pull-up resistor is needed on each of SDA and SCL. With the added bus capacitance, I would recommend no higher than 4.7K, with 3.3K not being unreasonable for a 3.3V supply.

    -Phil
  • sunblocksunblock Posts: 55
    edited 2012-10-30 23:14
    I feel so jazzed, thats what I figured. This stuff is fun! Is there a one or two code liner that would tell you if the EEPROM was actually "on line" for lack of a better term? The View Info doesn't seem to list anything beyond the base 0 EEPROM. I was looking for something kind of like the "PUB Nothing" command for smoking the EEPROM.

    Sunblock
  • RobotWorkshopRobotWorkshop Posts: 2,307
    edited 2012-10-31 09:40
    Hello Sunblock,

    If you are using a board with the DIP-8 version of the EEPROM then you could use one of my small adapter boards. You can either leave the jumper in place and let it keep each chip at different addresses or use it as a bank switch adapter to install an extra chip so you could have a couple different programs loaded in it and just switch between them

    http://forums.parallax.com/showthread.php?126798-NEW-EEPROM-expansion-%28bank-switch-adapter%29
  • Mike GreenMike Green Posts: 23,101
    edited 2012-10-31 12:04
    Look at Basic_I2C_Driver in the Propeller Object Exchange. The ReadPage method attempts to read a byte from a specified EEPROM address. If there's no device at that address, it will return a non-zero value. When the routine sends the byte address out on the I2C bus, it looks for an acknowledge bit returned by the device. If that's missing, it reports it as an error since that means that there's no device there to respond to the address.
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