[CSCI2321] set/reset latch

[John Howland]

The definition of set_reset which appears in log20050328
has a flaw.  What is the flaw?  Hint: try inputs of
0 1 (set) for both state values and inputs of
1 0 (reset) for both state values.

The following definitions (set-reset.ijs) and
(set-reset1.ijs) seem to fix the problem, but why?

Following are the definitions:

leda:/users/jhowland/cs2321 jhowland$ cat set-reset.ijs 
NB. a set-reset state object

state =: 0   NB.  Initially the state is zero
not_state =: 1

require_circuits_ 'circuits.ijs'

bitNor =: bitNot_circuits_ & bitOr_circuits_

set_reset =: monad define
'r s' =. y.
'state not_state' =: (bitNor r , not_state) , bitNor state , s
'state not_state' =: (bitNor r , not_state) , bitNor state , s
)

leda:/users/jhowland/cs2321 jhowland$ cat set-reset1.ijs 
NB. a set-reset state object

state =: 0   NB.  Initially the state is zero
not_state =: 1

require_circuits_ 'circuits.ijs'

bitNor =: bitNot_circuits_ & bitOr_circuits_

set_reset =: monad define
'r s' =. y.
(state =: bitNor r , not_state) , not_state =: bitNor state , s
state , not_state =: bitNot_circuits_ state
)


-- 
_______________________________________________________________
John E. Howland       url: http://www.cs.trinity.edu/~jhowland/
Computer Science    email: jhowland at ariel.cs.trinity.edu
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