Dataman S4 - Manual (Page 45)

DATAMAN S4 MANUAL
EMULATE KEY 45
written to the location in RAM specified by the
address bus. The 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
Byte-Wide RAMS may also be emulated. If the
EMULead is to be plugged into the socket
meant for a STATIC RAM, the PROM
configuration must be set to a PROM which
has similar address and data pin-out. The