Re: ROM 3 Questions

[dempson@actrix.gen.nz (David Empson)]

william strutts <wrstrutts1@home.com> wrote:

> "David Empson" <dempson@actrix.gen.nz> wrote in message
> > 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?

It doesn't involve the PRAM, so the condition of the battery shouldn't
affect the appearance of these CDAs.  The only factor is the contents of
a specific memory location in bank $E0 or $E1.

Power supply loading might have an effect on the dynamic RAM startup
state, so the installation or removal of a power hungry card like the
RamFast might influence this (but I doubt it).

> The 28 pin ROM has these numbers on them:
>     TC531000CP-F738
> 
> The longer ROM/PROM is marked Toshiba TC571001D-15 Japan
> 9015ECK.

The '531000' and '571001' parts strongly imply that the 28 pin chip is a
masked ROM while the 32 pin chip is a PROM.

The standard part numbers for an EPROM or PROM nearly always include a
'7' (e.g. 27C256, 27C010, 27C1001), with the distinction between an
EPROM and PROM being determined by suffixes or package types.  The
corresponding masked ROM almost always has a similar part number with
'3' in place of the '7'.

There are two standard pinouts for a 128Kx8 EPROM/PROM.  The most common
one is compatible with larger and smaller EPROMs/PROMs, allowing a
design to support mulitple capacities with room for firmware expansion.

The less common one (in my experience) has a slightly different
arrangement of pins which allows the EPROM/PROM to be replaced with a 28
pin masked ROM, as in the IIgs.