=A0Negative
logic design is usually not for the faint hearted ;)
I've owned PDP-8s for 70% of my life and I still struggle to really
understand the R-series stuff.
I cna't beleive it's worse than the HP9100 where the logic runs off a
-15V supply and the flip-flop inputs are current-operated (directly onto
the base of a PNP transistor). The emitter of that transistor goes to a
not-so-negative rail (-2.4V or something like that).
The diode-and-resisotr AND gate looks like this
Input A ----->|------+-----|<------- Output
|
Input B --/\/\/------+
4k7
Basically, Current will be sunk form the output (thus turning on the
flip-flop input transistor provided input B is -ve (to provde a path for
the curren throug hthe resistor) and input A is -ve (if it's ground,
the currne will be drawn through the left hand diode, the right-hand
diode will be cut off (remmeber the trnasitor emiter returns to a -2.4V
rail).
-tony
