where to find info

[Jemison Richard]

If I could elaborate a bit here.  PROM is actually (P)rogrammable (R)ead
(O)nly (M)emory and refers as is described below to a non-volatile memory.
However, it was based on tiny fuses which were (1)s if you left them alone
and (0)s if you blew them (you could also get reverse logic proms).

The prom was laid out in a matrix of addresses of a specific word length.
To program them you specified an address and the "value" or the word.  Every
bit which was a 1, the programmer would blow the fuse.

These were very cheap compared to EPROMS but were definitely one shot
devices.  Programming changes required new PROM chips.  Hope that helps.

Rick

> -----Original Message-----
> From:	ron.boley [SMTP:ron.boley at worldnet.att.net]
> Sent:	Sunday, November 01, 1998 7:11 AM
> To:	diy_efi at efi332.eng.ohio-state.edu
> Subject:	Re: where to find info
> 
> Geoff,
> 
> You need to look at some of the semiconductor sites.  Intel, AMD,
> National Semiconductor and more.  The generic term implies a
> non-volitile memory device (doesn't loose it memory when the power is
> removed).  Early versions 70' and '80s were based on UV-Erasable
> technology (Ultaviolet light they have quartz windows in them) others
> were EEPROM (Electronically Erasable Programmable Read Only Memory). 
> Flash memory came out in the early '90's which has generally replaced
> the older EPROM and EEPROM is most devices.  The beauty of Flash and
> older EEPROM is that it could be erased and reprogrammed while in a
> device where as EPROM usually required removal.  Todays FLash devices
> (Intel and AMD) have multiple sections where you can both store code and
> variables, as well as keep the latest change data on the product.  AN
> example on an ECC might be run the car and collect OBD-II data.  In many
> cases engineers may combine Flash memory with a smaller EEPROM.  The
> flash holds the program while the EEPROM holds the every day data
> (OBD-II).  I hope this gets you started.
> 
> Ron Boley
> 
> 
> Geoff & Sue Richards wrote:
> > 
> > Could someone be able to tell me of any books or web sites that can
> explain
> > the workings of a prom?
> > I have searched the archives in vain,any references to proms are for
> those
> > that already know how these work
> > I would like to understand addresses and maps etc
> > TIA
> > Geoff