Datasheet

D-TYPE FLIP-FLOP AND LATCH SIGNAL CONVENTIONS
1–12
POST OFFICE BOX 655303 DALLAS, TEXAS 75265
It is normal TI practice to name the outputs and other inputs of a D-type flip-flop or latch and to draw its logic symbol
based on the assumption of true data (D) inputs. Outputs that produce data in phase with the data inputs are called
Q and those producing complementary data are called Q
. An input that causes a Q output to go high or a Q output
to go low is called preset (PRE). An input that causes a Q output to go high or a Q output to go low is called clear
(CLR). Bars are used over these pin names (PRE and CLR) if they are active low.
The devices on several data sheets are second-source designs, and the pin-name conventions used by the original
manufacturers have been retained. That makes it necessary to designate the inputs and outputs of the inverting
circuits D and Q.
In some applications, it may be advantageous to redesignate the data input from D to D or vice versa. In that case,
all the other inputs and outputs should be renamed as shown below. Also shown are corresponding changes in the
graphical symbols. Arbitrary pin numbers are shown.
S
1
C1
2
C
6
Q
5
C1
1D
3
D
R
4
Latch
PRE
CLR
Q
S
1
2
CLK
6
Q
5
1D
3
D
R
4
Flip-Flop
PRE
CLR
Q
R
1
C1
2
C
5
Q
6
C1
1D
3
S
4
Latch
Q
6
5
Flip-Flop
PRE
CLR
Q
Q
D
R
1
2
CLK
1D
3
S
4
PRE
CLR
D
The figures show that when Q and Q exchange names, the preset and clear pins also exchange names. The polarity
indicators ( ) on PRE and CLR remain, as these inputs are still active low, but the presence or absence of the polarity
indicator changes at D (or D
), Q, and Q. Pin 5 (Q or Q) is still in phase with the data input (D or D); their active levels
change together.