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DATAMAN S4 MANUAL
micro would happily try to write to ROM, if
required to do so, but
nothing would happen because the ROM has no
WRITE input.
Correct Prototype Design
There are many microsystems around which are
incorrectly designed.
A common mistake is to select the memory chips
by their OE inputs
instead of CS. Another mistake is to connect OE to
CS - or even
to ground. CS should be derived from the
ADDRESS bus, and OE should
be derived from the READ STROBE. Systems
designed without regard use
more current than they need to. There is a period
of conflict in every
cycle, in which both the micro and a memory chip
are enabled on the
bus together, and this causes current surges and
voltage spikes.Some
memory parts require longer access times when
recovering from such
conflict. Access time is also worse if the system
does not apply
CS prior to OE - access time from OE is always
shorter. ROM emulation
will work in such systems - but RAM emulation
cannot work if the
system does not apply CS without OE - nor would
it work with a real
RAM. Chip Select must be TRUE, and Output
Enable FALSE when writing.
Emulating RAM.<$IEmulating RAM>
EMULATE KEY
47
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