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 M5L2764 EPROM Programming Fix

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T O P I C    R E V I E W
Krankshaft Posted - 11/18/2015 : 20:37:03
I recently had an older Mitsubishi M5L2764 N-MOS EPROM I needed to read to backup the firmware in a vintage Keithley multimeter. This thing was cool looking I've never seen an EPROM with a raised window before.

The device was already listed in the software however it didn't read properly (intermittent bits were corrupted) or program correctly (unable to write past 8%).

I was able to fix this issue and I am now able to read and program it with my GQ-4X. I fixed it by updating the device definition in the devices.txt file in the GQ installation directory.

Before I begin external power to the programmer (9 volts) is REQUIRED when programming this older N-MOS EPROM it's quite the power hog (I measured peaks of 140ma when programming on my bench supply). Way more than the USB port can provide. This was already specified in the definition file so you're told to apply external power when the device is selected.

Originally the M5L2764 text line looked like this:

Name="M5L2764",ID="XXXX",Class="2764(21V Vpp)",Category="EPROM",MFG="Mitsubishi",Message="Apply external power !";//by EZo

The issue with this is VPP MUST be at 5 volts when reading (it originally was undefined) this explained the read issue.

As for the programming issue VCC MUST be at 6 volts when programming. The 21 volts on VPP when programming already there was fine. All of this is listed in the manufacturer datasheet.

Since the GQ-4X can't provide 6 volts VCC I chose 6.2 volts although this data sheet didn't specify the VCC read voltage tolerance it's usually +- 0.25V so 6.2 is within tolerance.

So simply delete the old text line and copy and paste this one to get this EPROM to read and program properly.

Name="M5L2764",ID="XXXX",Class="2764(21V Vpp)",Category="EPROM",MFG="Mitsubishi",VCC="5V",WVPP="21V",WVCC="6.2V",BVCC="5V",RVPP="5V",Message="Apply external power !";//by EZo

Also a question for ZLM or anyone knowledgeable the read VPP before I defined it for this chip was originally listed in the GQ program (click the i button next to the device part number) as "undefined" what does that mean? Does that mean no power is applied to VPP when reading just curious?
4   L A T E S T    R E P L I E S    (Newest First)
Lan Di Posted - 03/07/2018 : 01:18:40
Thanks, Krankshaft. Your solution helped me avoid losing time and unwanted hassle.
ZLM Posted - 11/23/2015 : 20:32:27
If RVPP is unspecified, the the state will be low.

Name="M5L2764",ID="XXXX",Class="2764(21V Vpp)",Category="EPROM",MFG="Mitsubishi",VCC="5V",WVPP="21V",WVCC="6.2V",BVCC="5V",RVPP="5V",Message="Apply external power !";//by EZo, added RVPP,WVCC by Krankshaft
Krankshaft Posted - 11/22/2015 : 06:14:59
I also added the proper WVCC originally it was 5 volts which caused writes to the EPROM to fail. Changing it to the data sheet specified 6.2 volts allowed it to be written to successfully.

So when the RVPP is unspecified it won't apply anything to VPP when reading? Just making sure I understand.
ZLM Posted - 11/21/2015 : 09:39:54
Thank you for your update.

The RVPP means apply RVPP to the VPP pin while reading.

"undefined" means not specified.

Now the definition line will be:

Name="M5L2764",ID="XXXX",Class="2764(21V Vpp)",Category="EPROM",MFG="Mitsubishi",VCC="5V",WVPP="21V",WVCC="6.2V",BVCC="5V",RVPP="5V",Message="Apply external power !";//by EZo, added RVPP by Krankshaft


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