Re: ROM 3 Questions

["william strutts" <wrstrutts1@home.com>]

"David Empson" <dempson@actrix.gen.nz> wrote in message
1evzxdp.nrjk3fwb8hxcN%dempson@actrix.gen.nz">news:1evzxdp.nrjk3fwb8hxcN%dempson@actrix.gen.nz...
> william strutts <wrstrutts1@home.com> wrote:
>
> Are you sure about the "341-0748" numbers being the same in both cases,
> but in a different socket?  That can't be right, unless someone has
> mislabelled one of them.  The same part number in a different socket
> implies the ROM is in the wrong socket, but the machine wouldn't start
> up in that case.

Machine 1:
  341-0748
  341-0728

Machine 2:
  341-0748
  341-0737

You're right I listed them in opposite order according to my notes
I had written down.

> I assume you've just listed them in opposite orders, and the ROMs in
> question are actually in the same socket.
>
yes

<snip>
> The Visit Monitor and Memory Peeker CDAs are available on all ROM 1 and
> ROM 3 machines, but they aren't supposed to be visible until you go into
> the monitor and use the # command.

Would this happen if the PRAM battery was dead too? Or due to the
installation of a RamFAST card?

<snip>
> > Why is there the obvious chip size difference between the ROM's?
>
> The type of ROM chips normally used in the IIgs are a 28-pin 128Kx8 mask
> programmed ROM.  Mask programmed ROMs are the most reliable type, but
> they are only cost effective if produced in large quantities (thousands
> at a time).

The 28 pin ROM has these numbers on them:
    TC531000CP-F738

> For prototyping and development purposes, Apple would have used EPROM
> chips (Erasable Programmable Read Only Memory).
>
> An EPROM requires at least one and sometimes two pins which are not
> required on a mask programmed ROM: programming voltage and program
> enable.  (Some also have an output enable pin, separate from the
> required chip select pin.)
>
> For a 128KBx8 EPROM, the minimum number of pins you need is 17 (address)
> + 8 (data) + 3 (power, ground, programming voltage) + 1 (chip select).
> This gives a total of 29, so there is no way you can use a 28 pin
> package for this capacity EPROM.  The next largest standard package size
> is 32 pins.
>
> After the development phase, if Apple was producing a small number of
> machines for an initial production run, they may have used PROMs instead
> of masked ROMs (much cheaper for small quantities).  The type of PROM
> used would have been identical to an EPROM, except it comes in a plastic
> case (EPROMs are ceramic) and would be missing the window for erasing.
> Since it has the same signal requirements as the EPROM, it would also
> need to be in a 32 pin package.

The longer ROM/PROM is marked Toshiba TC571001D-15 Japan
9015ECK.

> The ROM 3 motherboard (and possibly also the ROM 1 - I haven't looked
> recently) has provision for using either a 32 pin EPROM/PROM or a 28 pin
> masked ROM.  A 28 pin chip goes in the bottom end of the socket, so
> there would be four unused pins at the top.

--
--
William R. Strutts - wrstrutts1@home.com - Whatever!

C'est moi!  http://www.facelink.com/wrstrutts

Just hacking away...