Programming 27C64 with TL866 II - Plus

[tony359]

Hello all,

I have purchased a XGecu Pro programmer (TL866 II Plus) and I am testing it with some eeproms I have. I can successfully read and write an Atmel AT29C010A (so I know the device works) but when it comes to some old Fujitsu MBM27C64-30 I can only read them but not program them.

Fogive me my ignorance: I understand these eeproms need to be UV erased before they can be programmed. I do not have an UV lamp but this chip is completely blank and it passes the "blank check" from the software. Still, when I try to program it, it won't work.

Am I doing anything wrong here or are those chips defective?

Thank you!

[wraper]

TL866 II Plus provides up to 18V prigramming voltage, MBM27C64 requires 21V.

[tony359]

Hi Wraper

I thought the "C" version was only 5 Volts?

Edit: no you are right. It says the programming mode is entered when 21V is applied to some pins. So why is the chip listed in the software database??

[NivagSwerdna]

I understand these eeproms need to be UV erased before they can be programmed.

When factory fresh they are already in erased state and can be programmed straight away.

I use an old crusty programmer for these devices (Stag PP39) due to the voltage requirement.

[tony359]

Thanks - I now understand the erasing/programming procedure.

Is there a more modern alternative to those chips which does not require UV and which does not require 21V?

Cheers!

[NivagSwerdna]

AT28C64B but obviously the pin out will differ so you need to create a small adapter board

If this is not completely off-piste you might find someone has already done one.

[tony359]

I see

What about just giving 21 volts to the VPP pin via an external PSU? If I understand correctly programming is 5V and 21V are needed to enable the program mode. I think I may have seen a video online about that

[edavid]

AT28C64B but obviously the pin out will differ so you need to create a small adapter board

Why would you need an adapter?  The pinout was obviously intended to be compatible.

[wraper]

I see

What about just giving 21 volts to the VPP pin via an external PSU? If I understand correctly programming is 5V and 21V are needed to enable the program mode. I think I may have seen a video online about that

It's not like you can permanently apply 21V to Vpp. Voltage should change between Vcc and 21V at the right moment.

[Ian.M]

It probably doesn't even drive Vpp above Vcc as the software knows it cant reach the +21V programming voltage.  If it did, it would be theoretically possible to design a Vpp booster which would switch in an external supply when the programmer outputs a Vpp signal >> Vcc.  However it would almost certainly be less trouble to get or build (maybe Arduino Mega based), a programmer capable of +21V Vpp

[tony359]

The pinout seems compatible - VPP is missing but I suppose it's not needed anymore?

@Wraper
Got you.

In fact I started designing my own programmer some time ago but I could never finish it. It's on my to do list to make a readable schematic and ask for your help!

[tony359]

I happened to watch a video today where a guy was programming those eeprom with the UV window. I could spot the model number from a close up and did a search: that was a 12.75V unit! I went back on my Apple //e ROMs and they too say 12.75V. Shall I assume that those can be successfully programmed with the TL866?

[NivagSwerdna]

MBM27C64-30 datasheet says... +21V for programming

am2764adc datasheet says.... 12.5V for programming

Different question... different answer

[PCB.Wiz]

I happened to watch a video today where a guy was programming those eeprom with the UV window. I could spot the model number from a close up and did a search: that was a 12.75V unit! I went back on my Apple //e ROMs and they too say 12.75V. Shall I assume that those can be successfully programmed with the TL866?

Yes, the Vpp details matter. 12.75V is more modern / common.
You might find larger EPROMs that can fit into the same footprint. 27C64 is quite old, and small, so will have EOL'd a long time ago.

eg AT27C256R seems to be the cheapest/smallest OTP EPROM currently stocked
Winbond used to make MTP EPROMS  W27C512 in 28 pins, but for new designs in 2020, you might choose a Flash part instead.