46
Progr
a
mming
Many designs for
Eprom programming units have been published. Some are very good,
some mediocre. All work well, within their limitations. All the units, commercial or home
built, which connect to a PC are very versatile because you have the full programming
power of the PC to assist. Usually you can type the HEX codes directly into the computer
memory, then "dump" them into the
Eprom. It is also possible to save the relevant section
of memory to disc or tape. In addition you may be able to write simple routines for
converting decimal to binary or to swap the bits in each binary code, as described
previously, to simplify the hardware design of the Eprom board. Most computers can
convert readily between decimal and HEX, thus eliminating even this simple task.
If you intend to buy one then get the best programming unit you can afford. Most of the
units sold for connection to a Personal Computer (PC) are quite intelligent and use a
friendly Menu system to guide you through the necessary choices. They all comprise a
printed circuit assembly, usually in a box, which you must connect to the computer, and a
software package on disc or Eprom. The box will contain a socket - usually only one -
which permits easy insertion of an Eprom by releasing a locking tab or lever. It may also
contain a number of option switches, although the better models use internal switching
which
is controlled by the software. Usually, the box will need a supply of
mains
electricity.
O
ptions
You will be required to choose the options, which normally include setting a switch or
pressing a computer key, to choose the part number of the
Eprom (2716 etc.) and the
programming voltage. Three programming voltages are used: 26 volts 21 volts and 12.5
volts, the latter sometimes (but not always) being designated by an "A" suffix to the
Eprom
part number, for instance the 27128A. An immediate exception to this "rule" is the
2716A
which programs at 21 volts. Failure to choose the correct voltage can destroy the Eprom or
even damage the programming unit
, consequently you MUST consult the manufacturer's
literature.
In the very cheap units you may not have the option of 12.5 volts and the choice
of Eproms will be restricted to those of certain sizes from specific manufacturers, whilst in
the more expensive units you are likely to be asked, by the software program, which
manufacturer's device you have so that the programming pulses can be set accordingly.
They might also perform the programming in a much shorter time.
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