| T O P I C R E V I E W |
| magloman |
Posted - 06/18/2009 : 05:11:55
Hi,
I have LARGE problems programing M27C256B and it has been so for a long time now.
Today I recieved a new batch of eproms and it is still same problems.
Often it is write error or verify fail.
I have tried using 1k resitor between #14 and #20 according to other post here on the forum. It felt like it worked for some time but now is it bad again.
Nothing helps.
Always use blank check.
Tried using settings for 27c256, m27c256b, st27c256, 27256 and using resistor or not. Speed usually set at 0.
Other eproms works better. Like 27c512, 27c128 and m87c257
One of the latest errors was:
1.) Write fail at 0x0075FF, buffer=0x02, device=0xFF at around 90%
2.) Verifyfailed at 0x00007F, device=0xFF, buffer=0xC0
3.) Now it frooze at 49% and the red LED was still on. hade to remove the USB cable to unfreeze it.
4.) Hangs at 1% with red LED on. Have to remove the cable. (this is very common problem)
Sometimes, very rare it works. Maybe one out of 10 or more.
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| 8 L A T E S T R E P L I E S (Newest First) |
| ZLM |
Posted - 06/27/2009 : 18:08:28
looked the datasheet again.
Yes, you are right. the 27C128 can be replaced by 27C512 with offset C000.
See
Image Insert:
30.75 KB
Assume the pin 1 and 27 will be stay high when reading in your machine. Then the chip can be replaced by 27C512 with offset C000. |
| magloman |
Posted - 06/27/2009 : 13:16:45
quote:
Originally posted by ZLM
The 27C512 can not be used to replace the 27C128.
Are you really sure about this ?
I know for fact that you can replace 128 with a 256, and since the 256 can be replaced by a 512 it must work !
Am I so wrong in my thinking here ?
When replacing a 128 with 256 you program the "upper" area by using offset 4000.
meaning that to put a 128 at the "upper" area in a 512 should be 4000 + 8000 = C000
Anyone else care to comment too ? |
| magloman |
Posted - 06/27/2009 : 11:43:58
OK, thanks for the answer.
But IF I program the 256 bin file WITH the offset 8000, will it work too ?
/M |
| ZLM |
Posted - 06/27/2009 : 09:24:54
You can use 512s to replace 256s directly without set offset.
1. Select 27C512 from software.
2. load your data file (originally for 27C256)
3. program you 27C512
4. put the 27C512 into your 27C256 socket for testing.
The 27C512 can not be used to replace the 27C128. |
| magloman |
Posted - 06/27/2009 : 00:48:14
I have trouble writing 128s as well.
but 512s with 1k resistor works like a charm.
Can I use 512s writing 256s with offset 8000 and 128s with offset C000 instead ?
Will it work in my equipment then ?
In that case I no longer need to buy 128s and 256s at all. Hence my problem goes away.
 |
| magloman |
Posted - 06/25/2009 : 12:20:13
I have tried some more now. Did not find any pot, so I had to use regular resistors.
Tried 180, 680, 860, 1000 Ohms using different settings by selecting different devices in the list.
Best results selecting st27c256 as device and 860 or 1000 Ohm. Speed set to 0. Will almost always write but will also give "Verifyfailed at 0x00007F, device=0xFF, buffer=0xC0" always the same adress.
I have about 20 pcs of new and erased proms. No difference.
I give up now. I just ordered a new gq-4x from ebay, I hope it will help me solve this issue.
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| ZLM |
Posted - 06/18/2009 : 22:09:07
I had a few 27C256B chips with this problem. However,after retested them recently, they are all working good. I suspect this problem only happened on new chips. After a few times UV erase and write, then the problem may go away. The 1K resistor workaround is the right way to do. But some chips may need even lower value resistor. So, try 680 - 980 ohm resistors. Put a 1K potentiometer(varible resistor) may be a good idea.
If you want, you can send me 2 chips for testing. I can send you back after testing. |
| Bad_Ad84 |
Posted - 06/18/2009 : 16:37:27
send one to zlm so he can take alook |
