[Coco] About those EPROMS...

Salvador Garcia ssalvadorgarcia at netscape.net
Wed Apr 8 21:44:30 EDT 2015


Thanks Mark! The info is much appreciated. This is just a learning exercise. I handled EPROMs a long time ago. The current related discussion just brought this back.


Funny story for you all. I was burning an EPROM with one hand touching the burner. While the burning took place I was chatting with some one about some information that was displaying on the CRT screen and I pointed out something by touching the screen. I heard a loud pop and the EPROM burner never worked again :-S. I was exasperated. These were hard to find and expensive.



Salvador



-----Original Message-----
From: Mark McDougall <msmcdoug at iinet.net.au>
To: CoCoList for Color Computer Enthusiasts <coco at maltedmedia.com>
Sent: Wed, Apr 8, 2015 7:17 pm
Subject: Re: [Coco] About those EPROMS...


On 9/04/2015 9:09 AM, Salvador Garcia wrote:

> I found this
> instructable:
http://www.instructables.com/id/EPROM-reader/ However,  I
> would hopeto find
something better as it is not my idea to address the
> EPROM one addressat a
time!

You can buy really cheap programmers on the net. Not worth doing it
yourself 
unless the point is to learn how to do it...

> Only threecontrol
signals: /PGM, /OE and /CE. For normal use keep
> /PGM high and to readget the
address on the bus and bring down /CE and
> /OE. The documentation doesnot
specify what the difference between these
> two signals is or what happens ifI
tie them together and just bring them
> down at the same time. It also does
notmention if these inputs are high
> (or low) if not connected (or HiZ);

The
leading 'slash' character denotes active low. It is sometimes denoted 
using a
trailing 'hash' character. eg. CE#

CE# is the chip enable, and must be low for
the chip to respond to accesses.
OE# is the output enable, and must be low to
read data from the device.

Depending on the way you're using it (the circuit
and driving logic), and 
the device itself, these signals (CE#,OE#) may be tied
to GND, tied 
together, or driven independently. Generally in a microprocessor
application 
CE# would be driven by address decode logic (and possibly qualified
by other 
CPU control signals) and OE# would be driven by a CPU READ strobe (or
in the 
absence of one, an inverted WRITE strobe).

If you're designing your own
dedicated 'dump' circuit, and you're never 
driving the data bus, you could in
theory tie both to GND. Just be aware of 
setup and hold times when reading the
data.

Regards,

-- 
|              Mark McDougall                | "Electrical
Engineers do it
|  <http://members.iinet.net.au/~msmcdoug>   |   with less
resistance!"

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