Service manual

STP 11-25R13-SM-TG
Q - 33
e. Toggle Flip-Flop (T FF)
. In the T FF, the output changes state every time an activating input is
applied. The T FF is often used as a connecting circuit. See Figure Q-30.
Figure Q-30. Toggle Flip-Flop
_
(1) Looking at the initial condition of the gates when Q = 0 and Q = 1, you can reason what will
happen when the T input goes high. AND
1
is disabled because Q = 0 which is fed back to AND
1
.
_
AND
2
receives an input from Q that is high, enabling AND
2
when a high arrives. At this time, b goes high
_ _
and causes Q to go low which causes Q to go high. Now, due to Q and Q feedback, AND
1
is able and
_
AND
2
is disabled, resulting in Q going low and Q going high on the next T pulse.
(2) The T FF can be used as a nonsync connector or dividing circuit. Sometimes it is desirable to
have the output in a desired state before operation begins. So a S (direct set) and R (direct reset) are
provided.