DATAMAN S4 MANUAL
46
EMULATE KEY
dumped to a specific area of USER RAM where
they can be inspected. The
microprocessort in the target system can WRITE
as well as READ. It
it true that PROMS do not have a WRITE input,
but that is provided
separately on a flying lead.
<$IMemory Emulation;How memory
is selected>Microsystem
memory selection
In a microsystem, ROM and RAM are selected by
decoding the address
bus to derive unique CHIP SELECT signals. Each
chip has its own slot
in addressing space. ROM and RAM output their
data on the system
bus when their address is selected and the
microprocessor's READ line
becomes true: the READ line should be connected
to the OUTPUT ENABLE
lines of all chips in the system. The
microprocessor sees no difference
between ROM and RAM, when reading. During a
WRITE cycle the READ line
stays false and no memory chip can output data on
the bus. This prevents
conflict with the data written by the
microprocessor. The WRITE output
of the micro is connected to the WRITE input of
the RAM. When the
WRITE signal becomes true the write-data output
by the microprocessor
is written to the location in RAM specified by the
address bus. The
