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_at_p850ug1.demon.co.uk>
To: <classiccmp_at_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
>
>
Received on Tue Jul 10 2001 - 17:05:10 BST