Elektor EPROM, Руководство пользователя

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MICRO PROCESSOR
12 Elektor Electronics 11/2002
An EPROM emulator is a useful if not indis-
pensable tool if you are into developing soft-
ware for a system employing an EPROM for
storage of executable code or fixed data. Such
a ‘programmable imitation EPROM’ obviates
the need to erase an EPROM after any pro-
gramming cycle, before the new (and hope-
fully improved) program may be loaded into the chip. Erasing an EPROM with
the aid of UV light usually takes
about 20 minutes, which, many of
you will agree, is an annoyingly long
time. If you want to test a new ver-
sion of the software during those 20
(long) minutes, a second EPROM
may be useful, but the entire opera-
tion is still cumbersome and tedious.
Over time, many different EPROM
emulators have appeared on the
market.
Elektor Electronics , too, has
published a fair number of designs.
In most, if not all, cases, these emu-
lators are connected to the target cir-
cuit (sometimes also called host cir-
cuit) by way of a length of flatcable
terminated in a DIP-style plug that
can be inserted in an EPROM socket.
The length of the ‘umbilical cord’ is
limited to prevent a too high capaci-
tive load on the data and address
bus of the target system, or timing
problems caused by pulse reflection
on the cable. In practice, the con-
nection between the EPROM emula-
tor and the target circuit is often a
source of headaches.
A second, often neglected, disad-
vantage of the traditional EPROM
emulator is that it can not be pro-
grammed using a normal EPROM
programmer. Usually, programming
such units requires a special pro-
gram contained in the emulator soft-
ware (and hopefully supplied with
the kit).
The emulator presented in this
article goes off the beaten track and
is not hindered by any of the above
disadvantages. It can be pro-
grammed in any old EPROM pro-
grammer, and the complete unit may
be plugged into the EPROM socket
in the target circuit without any
problems.
EPROM Emulator
a perfect imitation-EPROM
Design by P. Goossens
As opposed to most other EPROM emulators, the design discussed in this
article provides a virtually perfect imitation of a ‘real-life’ 27C256 device,
which may be programmed in any programmer as well as inserted into
the target system.