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eprom studys...

Discussion in 'Microcontrollers, Programming and IoT' started by tedstruk, Jul 13, 2017.

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  1. tedstruk

    tedstruk

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    Jan 7, 2012
    I always thought that a prom had individual inputs that triggered specific outputs a bit at a time.
    I have connected a EPROM to my arduino to see how it works, and it appears that it is programmed for 1 byte only, and then is fired by enabling and disabling the outputs.

    so I decide if my devices need an on or off when it is in certain states, then enable or disable the chip to activate what ever?

    I can see how this little chip thing may have destroyed all humanity with its incredibly strange way of functioning, but I just don't see the use of an octopus in an airplane...

    Now being able to completely reset the octopus in 16hrs under a high intensity UV now thats a breakthrough!

    tell me oh great one... why am I under the impression that my chip has a complete set of circuits in it that I can control, when it just turns on or off?
    (This ain't no shift register man... just a eprom)
     
  2. kellys_eye

    kellys_eye

    4,282
    1,152
    Jun 25, 2010
    You can get serial EPROMs and byte-wise EPROMs.

    What's the type number of the unit you;re looking at?
     
  3. tedstruk

    tedstruk

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    Jan 7, 2012
    MX R 9401 27C512-15 M16550 KOREA Vpp12.5
     
    Last edited: Jul 13, 2017
  4. kellys_eye

    kellys_eye

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    Jun 25, 2010
    'Generically' that's a simple 27C512 device which has 64k x 8-bit of EPROM.

    There will be 16 address lines and 8 data lines.

    The contents of any of the 64k (65536 actually) 8-bit registers will appear at the output according to the 'address' you select on the appropriate address lines.

    Whether you use this to address just ONE bit of data per register or all 8-bits of data at any one time is up to you.

    Download a datasheet - the full specification and signals required to both WRITE to the device or read from it will all be noted and explained.
     
  5. AnalogKid

    AnalogKid

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    Jun 10, 2015
    An EPROM is a memory array, not a controller. Like any memory device, there are a number of bits grouped at each memory address location. Your devices has 65,536 locations, and 1 byte (8 bits in parallel) of data at each location. A combination of chip enables, output enables, and strobes force the device to present at its 8 output pins whatever data is at the address inputted at the address pins. You can use an EPROM as a programmable logic device, but don't confuse that specific application with the generic intention of the part.

    The first programmable logic devices were PROMs, repurposed to imitate a bunch of logic gates When EPROMs were invented, the idea took off and quickly spawned PLAs and PALs, the first parts designed from the ground up to be logic arrays. In the 80's I did a lot of designs with EPROMs as the logic core. Super reliable.

    ak
     
  6. tedstruk

    tedstruk

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    Jan 7, 2012
    Here in lies full of problems !
    I power the EPROM to read the individual bytes stored...
    bread board with 1k resistors for the LED's.
    It would seem that any input that is connected, should effect the byte shown,
    EXPLANE--- if I disconnect a resistor, it will kill an LED--> ? hence the LED burns out because of straight power through the chip with no resistance in the line. Chip enable is supposed to select the device. my test grid must be wrong... I need to wire each LED with its own resistance instead of resisting all the chip inputs, The chip would be testing OK, because all the lights--- lightup when all the inputs are resisted and all the outputs are HIGH (the LEDS light up!! ) I will need a better test bed than my present one>>>?!!? Will try and try again mr. wint...
     
  7. tedstruk

    tedstruk

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    7
    Jan 7, 2012
    Assuming the individual devices(input pins), the datasheet is talking about, receive a signal from the Chip enable(here after known as the CE), that input devices byte(the one programmed into the chip), should show on the lights....

    The button is at the OE(output enable) so I can put the chip into low power states (55%) by pushing it.. it is working good!

    but the lights are not changing when inputs are connected to the CE....
    The CE disables the chip when High and Highs the chip when Low.
    eg. all inputs are at TTL levels (transistor transistor logic?) what level are speaking of? 1 mv? signal only? fully grounded switch? how about circuit power? IMG_20170714_110309665.jpg
     
  8. AnalogKid

    AnalogKid

    2,543
    725
    Jun 10, 2015
    Your circuit cannot be diagnosed from your photo - or from *any* photo. Please post your schematic. Without it, we could go through 50 posts and get nowhere.

    ak
     
  9. kellys_eye

    kellys_eye

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    1,152
    Jun 25, 2010
    First - most chip activation signals are 'active low'. In other words you need to take the signal line to logic 0 (ground) to enable them - chip enable and output enable are both 'active low'.

    Second - you cannot 'drive' LEDs from the output lines. You CAN connect an LED via a resistor and PULL the line low to light it. The LED is therefore connected to the supply line then via a resistor to the data line on the chip. A resistor of around 1.5kΩ would be appropriate.

    Third - a 'blank' EPROM (wiped by UV or as from the distributor) is usually filled with FF(hex) in all memory locations so selecting ANY address line combination will result in all the LEDs lighting!

    But as ak says, post a schematic!
     
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