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Best Practices for EPROM IC Chip Programming

(3) Selecting the Right Device in the Software.
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IC Speed and Compatibility.
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The device selection screen
Programmer, Device selection

The right device needs to be selected from the list of devices in the software. If the wrong device is selected, the programmer may apply the wrong voltage to the wrong pins and may damage a device.

For example, if you have a 2764A, you cannot select a 2764, which uses a higher programming voltage.

Here are some hints on device selection:

(3A) The important part of a device name.

Programmer, Device selection

In general, the important part of a device name is the part before the dash '-'.

For example, you have this device made by ST: M2764A-3F1
then the important part is M2764A and you must make sure all the characters in the important part are in your selection, namely "M2764A". If you select M2764, then the wrong voltage will be applied.

Programmer, Device selection

(3B) Other parts of a device name.

What come after the '-' is not important as far as programming the chip is concerned. Those characters indicate speed, package type, leaded or lead-free, industrial or commercial temperature, etc. The s/w cannot list all of those combinations. If it does, the device list will be 25 to 100 times longer and impossible to scan with the human eye.

For package types, the software lists them in generic terms, with the '@' sign before it, such as @PLCC, or @SOIC, instead of the many different characters used by different IC manufacturers.

We just mentioned that the characters after the '-' is not important. THere is, however, exceptions. There are some PAL devices which use different voltages for programming different speed families. For example, a PAL16L8-5 is programmed very differently from a PAL16L8-10. In cases like this, the s/w displays them as different choices in the device list.

(3C) Long Device Names

Say, you have to program this device:
      AT25320B-SSHL-B
and you cannot find the exact thing in the s/w.
Applying the info from the previous items, you know that all you need to search is the part before the '-', namely AT25320B.

Another simply way to do it is to just copy and paste the entire name into the device selection dialog box. Initially you shall see no devices being listed.
Programmer, Device speed

Then you can begin by backspacing, eliminating characters from the right until devices appear. At this point, you can pick the physical form (IC package) according to what you need.
Programmer, Device speed

chip copy devices chip copy devices B

(3D) Helpful hints about device speed

Programmer, Device speed

Deciphering the speed from the part number is sometimes tricky for the novice. Hence a couple of pointers are given here.

For parallel memories (such as EPROMs, EEPROMs, Flash memories, but excluding bipolar PROMs) access speeds are normally 40 ns and up. Access speed is the time that the CPU has to wait for the data to be ready after it sends out the address signals to the memory. The smaller the number, the faster is the memory.

In the above examples:

200 means 200 ns,
20 also means 200 ns (it cannot be 20 ns, which would be fasters than 40 ns)
15 means 150 ns,
3 means 300 ns.

PALCE is a logic device. Logic devices are usually faster than 40 ns. Therefore, "20" for the PALCE is 20 ns.

(3E) Helpful hints about IC chip compatibility

There are many aspects about chip compatibility. For our customers, the following are the more useful hints, especially if you are dealing with maintaining or repairing of old equipment and are looking for IC chips to replace the defective ones.

(i) You can use a faster part to replace a slower part, but not vice versa.
For example, you can use a 55 ns EPROM to replace one that is 150 ns. Or you can use a PALCE22V10H-15 to replace one that is -25.

(ii) You have a GAL22V10-15 device in a circuit board. Someone told you that a PAL22V10-15 is drop-in pin for pin compatible. Yes, that is true for the circuit board. But it is a different story for using a programmer. For one, the later is not erasable, hence you cannot reprogram a used PAL22V10 as you do with a GAL22V10. Second, when you program the PAL part, you cannot use the GAL device selection, since the programming algorithms are not the same.

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