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With the chip in place, the first step is to load the code into a buffer prior to burning it into the EPROM. There are fundamental differences between the “non-standard” TMS made by Texas Instruments and ‘standard” s made by others. The UV wavelength used is the same as that used for sterilizing equipment. Be sure to check when ordering and make sure you get the UV-erasable version unless you want an OTP of course.
Here is one of my efforts regarding the latter. One is the READ voltage. Mask ROMS have embedded code that can’t be changed.
Fig 1 shows my eraser.
However the programming devices mentioned below do handle these other chips. The other voltage is the programming voltage Vpp. If things are OK, you’re done. For your average vintage microcomputer, EPROMS can be recognised by their clear transparent windows, normally covered by some kind of label.
The Willem requires you to set jumpers and dip switches whereas my TOP allows chip selection from software. The incorrect voltage can kill it. It’s almost completely unreadable. The ICs hold code, often an auxiliary program such as an application, utility or game which can be loaded immediately on startup.
Try 20 minutes first and if that doesn’t fully erase the chip try again with a longer interval until you find a time span that does. Don’t look directly at the bulb when the door is open. Make sure you know the specs you’re dealing with.
EPROM Technical Data
There are a number of programmers on the market. Often the pin-outs of the mask ROM will be different to the EPROM and some kind of “adapter” needs to be made to switch the pins around or the board circuitry altered. Epom to grips with EPROM programming, and having the gear to do it, is worthwhile if you want to maintain a vintage computer collection.
Usually a status bar shows progress. A couple of VCF folks helped me refine this article. Beware though, as many modern ones will not handle the smaller capacity ICs like the and ones found in very old microcomputers.
Typically, my eraser will blank a chip in about 20 minutes. A can hold 4k and so on. There are 27322 kilobits in a kilobyte. In particular make sure the Vpp is correct and that the IC is oriented correctly and in the right position on the IC holder.
TOPS software showing a binary loaded into the buffer and ready to go! This is applied to the Vcc pin and is typically perom volts. This is why the ICs have a clear window in them; to allow the UV light to penetrate and erase the data. It’s also inexpensive, is completely software driven and can supply all necessary programming voltages from a USB link. Modern programmers use menu-based interfaces that are easy to use.
These have a “C” between the prefix and size number e. Not just the size but also the manufacturer. Here is an important piece of advice. Otherwise there is great risk of zapping the ROM because voltage is applied to the wrong pin! After the prefix is a number such as 16, or 32, 64, etc.
EPROMS , , , , , , ,
The software that comes with the programmer will manage the burning process. They are cheap and flexible but have a bewildering array of jumpers and switches to set.
Once reprogrammed or “burned”they can hold their data for many years. There will be an icon or menu selection for this. These are explained in this Google Groups postingwhich also elaborates on the and series and how they differ from or, in the case of theare the same as 27xx EPROMS of the same size. Eprmo programmers appear popular fig 2.
Rather it provides enough practical tips and information for readers to attempt an EPROM replacement of failed compatible parts. From time to time those of us with the passion to preserve ancient computers from 2723 and s will come across the need to replace a failed masked ROM or EPROM.