The bipolar interface as shown has the disadvantage that it prevents
either side from powering off properly (and coming out of reset)
separately from the other. In my experience this turns out to be very
important. So using 2N7000s or LM339 (quad open collector comparators) or
bipolars as inverters (common emitter) is better for this. For low speed
the LM339 is almost the best choice imho. It also is un-fussy about supply
(up to 30V - see datasheet).

Peter

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