26 Mar
2002
26 Mar
'02
11:39 p.m.
A lot of manufacturers have thought it "clever" to rearrange the address and
data lines, on an EPROM, for example, in order to obfuscate their firmware.
It's not rocket science to trace the CPU<=>EPROM hookup, though it's also
surprising how few people are willing to take the 10 minutes to do that. You
can get some surprises with RAM, however, and particularly if you are trying
to "program" a battery-backed RAM for purposes of emulating an EPROM, since
the order of the addresses and data normally doesn't matter at all.
Dick
----- Original Message -----
From: "Hans Franke" <Hans.Franke(a)mch20.sbs.de>
To: <classiccmp(a)classiccmp.org>
Sent: Wednesday, March 27, 2002 2:36 AM
Subject: Re: ZX81 and 6116
> > line goes to which address pin on the SRAM, only that it goes to an
address
The same applies (of course) to data lines.
Provided each data lines goes
to _a_ data pin on the SRAM, it'll work. The data lines are bidirectional
on these chips, so if a bit is written on a particular line it'll be read
out on the same line. It doesn't matter what the RAM manufacturer called
it -- all data pins are equivalent on the chip.
Yep, true. The only situation I know where this has any
impact is if you use an in circuit RAM logger/emulator,
which picks the data from the RAM socket and of course
in all outputs assume that the lines are in 'standard'
use.
Gruss
H.
--
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