DATAMAN S4 MANUAL
EMULATE KEY 49
or outputs of 74HCT series gates via series
150<F128M>W<F255D> resistors within
S4: this minimises over- and under-shoot without
compromising output
drive too much. To prevent the lines floating
when disconnected,
which would cause unnecessary power dissipation,
all lines have 100K<F128M>W<F255D>
resistors pulling then to the 5 volt or ground rails.
To minimize
current-drain when emulating, it is preferable that
inputs should
be driven right to the 5v and 0v rails. Drive
current taken from
the data-outputs should be kept to a minimum.
<MI>S4 is impedance-matched to normal drive
conditions, e.g. direct
connections to output buffers. Emulation may not
work if driven with
high-impedance lines - via series resistors, for
example.
Emulating 2716 EPROMs
Due to a quirk in S4's hardware, 2716 EPROMs
must be emulated at address
00800, rather than 00000.<R>
<R>
This means that when loading a 2716 into S4's
RAM, which is intended
to be emulated, it must be loaded into addresses
00800-00FFF. This
is achieved by pressing the <F129M>a<F255D>
key when in the LOAD routine:
@COMPUTER TEXT = >>LOAD 2716<R>
00800-00FFF=00000
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