| T O P I C R E V I E W |
| vibroverbus |
Posted - 12/23/2011 : 06:47:06
Having trouble writing M87C287's and I see searching the forum a number of others have had difficulty with these chips as well.
Devices: M87C257-20XF1 & 20F1
Programmer: GQ-4X
Software: v.6.13 and v.6.14
Power: AC External power supply & voltage tests good
I have 20 supposedly "new ST brand" devices to test, 10 each from 2 different sources, and out of those only could successfully write 2 using the default settings. I was able to write 2 more using the M27C256B definition which has a very similar datasheet but lacks the latching feature. Failures are 90% during the write, 10% of the time the write completes but fails in final verify.
When reading Device ID on these chips using M87C287 setting, "FFFF" is returned which seems like a failed ID read process. When reading a blank using the M27C256B settings, "8080" ID is returned which is invalid but nonetheless seems better. Other old legacy M87C257 EPROMs I have DO successfully read a good ID using normal M87C287 settings however none of these "new" chips seem to read the ID with the M87C257 device settings.
The real ST datasheets for both devices seem to indicate the exact same procedure for interrogating Device ID so not sure understand why this is different.
I have customized devices.txt entries for these devices to ensure the voltages match datasheet and I am using lines as follows:
;********
Name="M27C256B#2",ID="9B04",Class="27C256",Category="EPROM",MFG="ST",VCC="5V",WVPP="12.7V",WVCC="6.2V",BVCC="6.2V",RVPP="5V",Speed="5"; //by JC
;********
Name="M87C257#2",ID="2080",Class="87C257",Category="EPROM",MFG="ST",VCC="6.2V",WVPP="12.7V",WVCC="6.2V",BVCC="6.2V",RVPP="5V",Speed="3"; //by JC
;********
Questions:
- Why does ID come back differently for different devices when datasheet indicates same procedure? Is there an error in the algo for the M87C257?
- Could these chips be fake re-labeled and actually be something else? They work in my application WHEN they burn so if there is a better device selection to try that would work it would be great. |
| 1 L A T E S T R E P L I E S (Newest First) |
| ZLM |
Posted - 12/23/2011 : 11:27:38
M27C256B and M87C257 are not compatible in read data mode. Reading ID uses read mode. M87C257 has to latche the address when reading the data and the ID. This is why you can not get the ID by 27C256B ID procedure.
M27C256B and M87C257 should be write compatible. When writing the address does not need to be latched on M87C257.
If you bought the chips from a not listed distributor of ST, then there are posibilites for "relabeled chips". Because those chips are not in procudtion for long time. The new chips are not easily to find. And they may come from a same root source. |
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