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EPROM Programmer.

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lord loh.

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Here is an old reference of my EPROM question

The EPROM programmer that I am designing has got two modes. viz Read / Programme.

The read mode has the following requirements:
Vcc=5v
Vpp=5v (programming voltage)


The programming mode has the following requirements:
Vcc=6v
Vpp=12v


The datasheet of the EPROM in question(M27256 8Kb) instructs that the Vpp be applied simultaneously or after Vcc. The VIL=Vss-0.1v and VIH=Vcc+1v

The solution I see to the problem is by using a 555 to provide the Vpp a short time (delayed start) after the switch is moved from the Read<->Prog. mode.

In the mean time the data and address from the counter shall be on the respective buses of the ROM. Can this potentially damage the ROM? ie. Supplying signals without the Vcc and Vpp. (I read that is is true for op-amps). Is the given protection circuit any good?

Could using a delayed start Vss be a solution? I guess not.

Can anyone please help me with my power supply unit....
Any tips or sample circuits will guide me.

Thank you.
 

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Nigel Goodwin

Super Moderator
Most Helpful Member
Why are you talking about 555's?.

Are you wanting to make a manual EPROM programmer?, where you have two rows of toggle switches (one for address and one for data), and a button you press to program a single location.

Generally you would do it from a computer or micro-controller/micro-processor, so the timing would be done in the computer - particularly as the programming usually requires multiple programming pulses, then a related number of over-programming pulses.

There's a design on my website at http://www.lpilsley.co.uk/misc.htm, which I found somewhere years ago, I've never built it, but it even includes the computer source code in Turbo Pascal.

Instead of using an antique EPROM, have you considered the modern replacements?, that don't require UV erasing - basically EPROM/FLASH in a pin compatible chip.
 

lord loh.

Member
:oops: :oops: :oops:

Yes... It is an antique EPROM programmer. I am litrally re-inventing the wheel. :( To make a microprocessor based programer, I must programme the microprocessor first. And for that I have the manual EPROM programmer.

This is supposed to be my Third year Project and I cannot change it at this late a date.

I do not have two rows of toggle switches. I have 4 7493 ripple counters that set the address. with individial increments that propagates to the MSB on overflow and individual resets that does not propagate.

Similarly two 7493s for data.

So I really must have a slow starter circuit for the Vcc Vpp. Can I drive a transistor with a series of inverters to act as a delay element...

Am I right to assume that transistors without a base resistors can work well as an on-off switch without producing any noticable voltage drop?

What is the best solution that I could go for in my existing project.
 

Nigel Goodwin

Super Moderator
Most Helpful Member
lord loh. said:
:oops: :oops: :oops:

Yes... It is an antique EPROM programmer. I am litrally re-inventing the wheel. :( To make a microprocessor based programer, I must programme the microprocessor first. And for that I have the manual EPROM programmer.
It's usual to program the EPROM from a computer, or aren't you allowed to do that either?.

This is supposed to be my Third year Project and I cannot change it at this late a date.

I do not have two rows of toggle switches. I have 4 7493 ripple counters that set the address. with individial increments that propagates to the MSB on overflow and individual resets that does not propagate.

Similarly two 7493s for data.
This sounds even worse than two rows of toggle switches!, how do you know exactly what address and data you are set to?.

So I really must have a slow starter circuit for the Vcc Vpp. Can I drive a transistor with a series of inverters to act as a delay element...
I'm not sure what you mean by a 'slow starter circuit', as for using a series of inverters?, how short a delay do you need?.

Am I right to assume that transistors without a base resistors can work well as an on-off switch without producing any noticable voltage drop?
Fed from what?, it's unusual not to have a base resistor, and would only normally be done if what's feeding it incorporpated a resistor or some suitable driver.

Do you mean for switching the programming voltage to the EPROM?, if so you can do it with an NPN transistor and a PNP one, plus three resistors.

What is the best solution that I could go for in my existing project.
We don't know what the limitations of your project are?, a simple answer would be to program a suitable PIC as an EPROM programmer, a 16F877 would probably have enough pins?.
 

Mike - K8LH

Well-Known Member
Not sure if this will help but you're welcome to glean whatever useful info' you can from this circuit excerpt from a 'burner' I made several years ago (yeah, I know it's crude)...

Good luck with your project... Regards, Mike
 

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lord loh.

Member
I have a six 'seven segment' displays for the address and the data.

The EPROM data sheet mentions that Vpp must be applied simultaneously or after Vcc. So to be on the safer side, I would like to apply the Vpp after a delay.

The slow starter circuit is to give the output after a small time delay. The output is triggered by switching the EPROM Writer from Read Mode to Programme Mode by a toggle switch.

I intended to have a circuit as toggle switch ->series of inverters for delay -> base of transistor.

Then the transistor gives the Vpp=12v to the EPROM device.

The limitation id that I have to demonstrate the project to the examiner at a place where I cannot have access to a computer. :( :( Forced into stone age. :(
 

lord loh.

Member
Yet another Reference
Nigel Goodwin said:
...This sounds even worse than two rows of toggle switches!, how do you know exactly what address and data you are set to?...
Well, Nigel, here is the final result of all discussions.
http://lord.loh.googlepages.com/eprom.html
You can see the picture of the EPROM Writer (Large Size Image) here and also the project report and circuit diagrams.
 

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