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 Vcc and Enhanced Willem
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grose

Canada
3 Posts

Posted - 10/25/2005 :  17:56:12  Show Profile  Reply with Quote
I just got the Enhanced Willem under the impression that it could do most of the 27CXX series eproms (as is EXPLICITLY stated in the documentation).

However, I did not discover the forum sticky until it was too late or I'd have ordered the dual power version.

Anyway the major issue is that Vcc on the enhanced is set a 5V from the USB and is not adjustable. ALL the 27CXX series eproms need 6V Vcc as far as I am aware. How could you market this thing with only Vcc of 5V? It means that NONE of the 27CXX are supported? By extension, NONE of the 27XX series are either. Do you not see a problem here?

Anyway, looking at the schematic for the PCB3B (which I'm assuming is similar in the power area as the enhanced), it looks like I could just use a regulated supply to put 6v through the usb power connector on the board and fix YOUR design deficiency. Is this the case?(lacking a schematic for the enhanced, I have to guess). The transistors look like the same small-signal type as on the Dual Power board.

Will this work?

Thanks

Edited by - grose on 10/27/2005 09:32:53
Reply #1

backbiter17

Slovenia
23 Posts

Posted - 10/26/2005 :  08:39:31  Show Profile  Reply with Quote
heve same problem
be careful with 6 V on input you can damage all chips which need 5V
br,ales
ps if you find any shematic of this programmer im interested also
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Reply #2

ZLM

2936 Posts

Posted - 10/26/2005 :  13:28:17  Show Profile  Reply with Quote
In pratical, most of 27CXXX EPROM will be programmed at 5V Vcc. If it does not, then increase the tWp will help the programming. So, the Enhanced willem will work for most of 27CXXX EPROMs.

I think it is safe if you use an external regulated 6V DC supply. All CD40XXX logic chips have wide range VCC: 3-18V. For some other 74HCXXX chips working voltage can up to 7V. As long as your voltage not exceed the 7V.

I have tested my Enhanced willem use a 6V external DC, and it works fine.

Based on PCB3B schematic, the 6.2V Vcc is applied to all logic chip too. And it works fine.



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Reply #3

grose

Canada
3 Posts

Posted - 10/26/2005 :  17:31:50  Show Profile  Reply with Quote
Thanks for the good info, here.

I tried to write a 27C256 and it failed on the first byte. I tried increasing tWp until it was at the maximum and still nothing.

I also tried to write a 16F84A which didn't work. It acted like it could verify the chip but I get "Error writing program area". Interestingly enough, it will verify the "chip" even if there's NOTHING in the socket. Pretty neat, huh? I assume that the PIC chip goes in the eighteen pin socket stuck in the middle of the 40 pin one? There is no real documentation to this thing.

So far, this thing is a bust. Anyone have any magic tricks to get this junk working?

I'm going to build a 6v adaptor tomorrow and see if that helps. I'm not holding my breath.

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Reply #4

ZLM

2936 Posts

Posted - 10/26/2005 :  22:11:33  Show Profile  Reply with Quote
There are some compatibility issues between the different manufactuer. All 27256 and 27C256 used same algorithm to write the EPROM. The only difference is the tWp and tWc. So you can try to select 27256 type with max tWp and tWc to write a 27C256, see if it works. If it still does not work, you may need to check if the programmer has the Vpp resented when writing.

Also, you need confirm your EPROM chip is not a damaged chip.

For the PIC chips, the programming will fail if you chip been code protected. Read it, see if the chip can be read. Also, you should be able to get the ID of the chip. The location of 28 pin PIC should be "Top Aligned" in the PIC Adapter+ ZIF socket.


Edited by - ZLM on 10/26/2005 22:23:40
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Reply #5

grose

Canada
3 Posts

Posted - 10/27/2005 :  05:04:48  Show Profile  Reply with Quote
Thanks ZLM,

I tried the 27C256 on max tWp and tWc and nothing works. I'm going to try another 27C256 to make sure this one isn't damaged somehow through my screwing around. I checked the Vpp on Test H/W and I'm getting 12.2V. I think this is a little low but I don't know if this is definitely my problem. When I remove the jumper and go to the 15V setting, I read 15V right on. I think 15V is a bit much for this chip though.

As for the PIC, it's brand new. The first time it was out of the package was yesterday. It's an 18 pin device so I thought it should go in the 18pin socket, but I don't know for sure. The graphic in the software doesn't even come close to what this board looks like. You would think that the people who SELL this board would provide at least some board specific documentation.

When I try to read the chip, it reads as blank. But as I said before, it does the same when there's no chip installed! I cand read the ID, but the last 4 digits are RED ?. I'm guessing that this chip is not connected right.

Can I use the ICSP for the PIC16F84A?

Thanks
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Reply #6

DL

USA
46 Posts

Posted - 01/18/2006 :  14:17:46  Show Profile  Reply with Quote
Hi ZLM,
quote:
Originally posted by ZLM

In pratical, most of 27CXXX EPROM will be programmed at 5V Vcc. If it does not, then increase the tWp will help the programming. So, the Enhanced willem will work for most of 27CXXX EPROMs.
This is a common misperception. An EPROM is actually an analog device. Whether you read a '1' or a '0' depends on how much charge is stored on the floating gate.

One aspect of reliability is will a programmed (or unprogrammed) bit read that way over the full VCC and temperature range. And, how long it will read correctly (charge loss can only be prevented by a perfect oxide which doesn't exist). Most manufacturers specify programming at a VCC higher than the normal operating VCC(max) - i.e. 6V. By doing this, you're guaranteeing that there's enough charge for programmed bits to read as programmed for a couple decades. Similarly, you need to do blank verification of used parts to make sure that the residual charge on the floating gate isn't sufficient to be read as programmed under low VCC conditions. You simply can't do this on a programmer with no VCC options and I don't know of any programmers that give you enough control to do these operations. I've modified several of my programmers to give me a variable VCC option so I can set any voltage I want. I also added a relay modification to address issues with voltage drop in the transistor switch (trying to control VCC to within 10mV is impossible with a transistor switch). You can find details on willem.org.

So, while what you say has some truth to it, it says nothing about creating reliable parts.

quote:
I think it is safe if you use an external regulated 6V DC supply. All CD40XXX logic chips have wide range VCC: 3-18V. For some other 74HCXXX chips working voltage can up to 7V. As long as your voltage not exceed the 7V.
Max VCC for at least one of the 74* bicmos families is 5.5V. Exceeding that could damage parts. Since no one has a schematic or component diagram and you can't be sure what chips are being used by the various sources of enhanced boards, you're taking a gamble by doing this...

EDIT: I checked a TI datasheet for 74HC and 74HCT. Devices are not guaranteed to *function* at voltages above VCC(max). For 74HC this is 6V, for 74HCT it's 5.5V. VCC(absmax) is specified as 7V for both families, but a footnote in the spec also says that operation above VCC(max) is not guaranteed.

On the other hand, CD4xxx are guaranteed to operate from 3-15V and VCC(absmax) is typically 18V.

Since most universal programmers have sanded part numbers, you can't be certain whether you have 74HC04, 74HCT04, or CD4060. I've seen some programmers (with part numbers intact obviously) that used 74HC14 or CD40106 schmitt inverters which helps with signal quality on computer output signals. Personally, I like the CD4049 better because it's better suited for driving 2 meters of wire back to the computer...


HTH,
Dennis

Edited by - DL on 01/19/2006 10:26:37
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Reply #7

ZLM

2936 Posts

Posted - 01/25/2006 :  15:05:29  Show Profile  Reply with Quote
Thanks DL for all useful information.
The Enhanced willem programmer is not the best for programming the UV type EPROMs. Especially it does not work on NMOS EPROMs. Since there is no schematic is available on it. So, please read the info from DL before doing the external DC testing.
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