[Coco] About those EPROMS...

[Mark McDougall]

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!"