10 Jul
2001
10 Jul
'01
10:05 a.m.
If you tie Vpp to Vcc through a 100-ohm resistor, you'll see that the device
uses the Vpp as a supply when it's selected. It will happily pull down that
100-ohm pullup. The device won't work under those circumstances.
On later EPROMs, i.e. the CMOS variety, you can use Vpp as an additional chip
select if you like. It's quite a common practice.
Dick
----- Original Message -----
From: "Tony Duell" <ard(a)p850ug1.demon.co.uk>
To: <classiccmp(a)classiccmp.org>
Sent: Tuesday, July 10, 2001 1:53 PM
Subject: Re: Correct installation of a 2716 eprom
Another simple question. When a standard single-rail 2716 is installed
in a computer, what do you do with the Vpp pin? Tie high, low, or
leave alone? If tying, what, if any value resistor should be used?
Connect Vpp to Vcc (+5V), with no resistor in series (i.e. a direct wire
connection). That's what I've always done anyway.
Is this answer different for masked ROMs or other
EPROMS?
With most EPROMs you link Vpp to +5V in read mode. Mask ROMs obviously
don't have Vpp line, and the pin is normally either unconnected (in which
case you can do what you like with it, within reason [1], including
connecting it to +5V), or sometimes it's another chip enable input. The
latter is often level selectable by an option set by the programming mask
(i.e. when the chip is mask-programmed, as well as the data being
defined, the active level of the chip select lines (active high or active
low) can also be set). Of course if the mask ROM has an active-low enable
pin there, you have to connect it to ground.
Is there a standard reference book or site that
answers questions like
this? I don't want to wear out my welcome :-)
What you need are the data sheets for the EPROM you are using. Most
semiconductor companies put the data sheets of their current parts on the
web in pdf format. Very rarely are obsolete data sheets made available in
this way.
It's worth obtaing all the old data books that you can find, since they
contain data sheets for the chips found in classic computers :-)
-tony