Alto Hardware Manual
Section 7: Ethernet
55
* These functions have a peculiar timing restriction associated with them. The microinstruction that
executes one
of
them must stop the clock for one cycle. On Alto I, the microprogrammer must do
this
using memory timing (i.e., by referencing
MD
in the same microinstruction, during the third
or
fourth cycle
of
a memory reference).
On
Alto II, the hardware automatically stops the clock for
one cycle when necessary; however, due
to
a design error, the instruction following the one
specifying
EIDFCf
or EILFCT
is
occasionally stopped instead. Consequently, the programmer must
not permit a task switch to occur between these
two
microinstructions,
nor
start a memory
reference in the following microinstruction.
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