[SOLVED] [moved] Reading mode for EPROM 27c128

[sherline123]

I needed to use this EPROM is my project. After storing values by using universal programmer, I tried to verify the values manually (by using oscilloscope and testing several address lines). I found that all I get is '1'. I tried read the values by using universal programmer and it shown the values which I stored. I am a newbie to use EPROM. I followed the datasheet. Connect the EPROM wrong way will cause all results getting '1'? Is there useful ways to allow me verify the values stored in EPROM?

 

[esp1]

Re: Reading mode for EPROM 27c128

hi 123,
Could you post your EPROM reading by scope circuit.?
Are you switching the R/W lines and Enb.?
E

 

[betwixt]

Re: Reading mode for EPROM 27c128

If the EPROM is selected and it's output enabled, the data pins will follow whatever is stored in the address selected by the address pins. I suspect you are not selecting the EPROM at the time you are looking for the data, the OE and CE pins must both be low for the data to appear at the output.

It doesn't have an R/W pin by the way :shock:

Brian.

 

[sherline123]

Re: Reading mode for EPROM 27c128

I connected both of them to ground all the time. btw, connect the EPROM in a wrong way will cause I read all values of '1's?

 

[Aussie Susan]

Are you saying that you inserted the EPROM into your circuit the wrong way around? If so you may well have destroyed it.
Also, looking at the waveform diagram (data sheet Figure 1-1 from https://www.jaapsch.net/psion/pdffiles/Eprom016k_datasheet_27C128.pdf), it looks like the high-to-low transition of the \CE\ line is used to read the address and the high-to-low transition of the \OE\ line is used to output the correct data. I don;t think you can simply hold these pins low (but I've never used these EPROMS and I may be mistaken).
Susan

 

[logu2289]

Dear sherline123,

can you post code for accessing this EEPROM? I will look into it.

 

[sherline123]

I am sorry, what is the code you meant?

 

[bigdogguru]

Do you intend on using this EPROM as external ROM in conjunction with a microcontroller/microprocessor?

Or will it be used to implement a Finite State Machine (FSM)?

Or something else?


BigDog

 

[andre_luis]

I tried to verify the values manually (by using oscilloscope and testing several address lines)

What exactly do you mean by manually ?
How did you make the manipulation of logic levels on pins ?

 

[FvM]

Also, looking at the waveform diagram (data sheet Figure 1-1 from **broken link removed**), it looks like the high-to-low transition of the \CE\ line is used to read the address and the high-to-low transition of the \OE\ line is used to output the correct data. I don;t think you can simply hold these pins low (but I've never used these EPROMS and I may be mistaken).

You read the data sheet wrong. All 27xxx are fully static, pulling OE and CE permanently low outputs data according to the present address.

VPP and /PGM pins must have the required levels, you must no leave any address line floating.

 

[sherline123]

I random put high (inserting 5v) to few address lines and check the output by using oscilloscope

some sort like FSM. but my quest is "in what conditions, the EPROM will show all values of '1's even after program it."

 

[bigdogguru]

As FvM indicated, you need to pull both CE and OE low, to ground, tie Vpp to Vcc and pull PGM high, to Vcc. Of course you will also need to apply Vcc to the Vcc pin and ground (GND) to GND pin.

An oscilloscope is probably not the best tool for this job.

Set ALL address lines high or low, you can use a pair of 8-bit DIP switches with some resistors for pull ups.

You can monitor the output data lines with a simple logic analyzer or use an octal line driver, to drive 8 LEDs.


When designing your FSM, you will need to employ an octal latch, like the 74HC373, to prevent glitches and possible race conditions.






BigDog

 

[andre_luis]

After storing values by using universal programmer, I tried to verify the values manually

Irrespective to your wish to do that manually, or even the purpose of "see it to believe it", you should be aware that most programmers already perform the verification of the data wrote. Take a look on its documentation to check if it is an unnecessary concern.

 

[sherline123]

ok. I just found out my results are correct when using battery as power supply. meanwhile, if i replaced the power supply with dc power supply generator, all of the outputs show '1'. I tried with several dc power supply generators in lab. Any ideas?

 

[betwixt]

As far as the EPROM is concerned, it makes absolutely no difference where it's supply comes from.

Please post a schematic of wht you are trying to do so we get a better idea of what is wrong.

I random put high (inserting 5v) to few address lines and check the output by using oscilloscope

begs the question what did you do with the other address lines?

Brian.