Examination of a rocker
D |
Use
of a rocker D like detector of positive transitions |
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Created it, 06/10/19
Update it, 06/10/24
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5. - SECOND EXPERIMENT : EXAMINATION OF A CIRCUIT ROCKS R.S. WITH ORDERING OF VALIDATION
In the following exercise, you will add an entry of order allowing to validate the two entries of rocker R.S. the order thus authorizes the taking into account of the two logical levels on the entries.
To carry out this new circuit, you will proceed in the following way :
a) Disconnect the food and remove all the connections established previously.
b) Carry out the new connections while referring to you with the figure 10-a and the following indications :
connect pin 1 of
ICX with pin 11
of ICX
connect pin 2 of
ICX with pin 6
of ICX and the L1
contact of the group of connectors (use the triple driver).
connect pin 3 of
ICX with pin 4
of ICX and the L0
contact of the group of connectors by using the triple driver.
connect pin 5 of
ICX with pin 8
of ICX
connect pin 9 of ICX
with contact SW1 of the group of connectors
connect pin 10
of ICX with pin 12
of ICX and the P0
contact 
of the group of connectors (conducting triple)
connect pin 13
of ICX with contact SW0
of the group of connectors.
c) Introduce the integrated circuit MM 74C00 into support ICX.
d) Put two reversers SW0 and SW1 in position 0.
You carried out the illustrated
circuit appears 10-b. This circuit comprises three entries R,
S, C and two exits Q and 
.
The entries S and R are on the level L thanks to switches SW0 and SW1. The entry C is also on the level L, because the P0 button is slackened. Ultimately, this circuit is a rocker RS preceded by two circuits NAND whose operation depends on the order C.
e) Connect the food : one of the two LED ignites (L0 or L1) without one being able to determine in advance which.
f) Carry out the various combinations with two switches SW0 and SW1. Note that there is no change of state on the exits of the rocker.
g) Put SW1 on position 0 and SW0 on position 1. Press on the P0 button and maintain it in this state. The entry C passes on the level H and makes it possible to validate the two NAND by pins 10 and 12. The two logical states on R and S are found reversed on the two entries corresponding of the rocker to pins 1 and 5. The LED L0 ignited.
h) Slacken the P0 button : the LED L0 remains lit.
i) Now put SW0 in position 0 and SW1 in position 1. There is no change of state on the two exits.
j) Support and slacken the P0 button ; L0 dies out and L1 ignites.
k) Continue the experiment by testing the various combinations of SW0 and SW1 and observe the two LED.
On the basis of data obtained with these tests, you can draw up the table of operation and extract the truth table from it from the circuit carried out, by adopting the procedure followed to the first experiment.
You can compare the results obtained with those deferred in the two tables of figure 11.
In those, symbols X indicate that the entries S and R can be indifferently on the level H or L (logical value 1 or 0) without influencing the state of the exit of the circuit, i.e. without determining swing of the levels of exit when the order C is on the level L.
You can yourself raise this result in practice by noticing that if the P0 button is not inserted, switches SW0 and SW1 can be commutated on any position without that determining a change of state of the LED.
On the other hand, if the P0 button is inserted, the state of the rocker depends on the levels present at two entries S and R.
In conclusion, you could by this experiment see how it is possible to obtain an improvement of rocker R.S. by the addition of two circuits NAND. You obtain a rocker R.S.C thus.
The characteristics of this rocker are as follows:
using the entry C,
it is possible to order the operation of the rocker. More precisely, if the
entry C is on the level L,
the rocker remains blocked with the state where it is, independently
of the variations of the levels applied to the entries S
and R. If the entry C
is, on the other hand, on the level H, the
rocker can commutate and take a state dependant on that of the entries S
and R.
If S and R
are both on the level L, even if C
is on the level H, the rocker does not
change a state. This configuration of the levels of the entries corresponds to
the at-rest state of the rocker.
If C is on the
level H, the entries are validated, i.e.
they have an action on the state of the rocker.
When S is on the level H and R on the level L, the rocker takes state 1, i.e. the exit Q is on the level H.
When S is on the level L and R on the level H, the rocker takes state 0, i.e. the exit Q is on the level L.
The advantage which rocker R.S.C offers is as follows : the signals applied to the entries S and R can cause a change of state of the rocker only when the authorization is given by it by the entry of order C.
Note that in this circuit, unlike that seen in the first experiment, the at-rest state is LL, that is to say S and R on the level L, and that the two entries are active on the level H. This operating mode is due to the inversion introduced by the first two NAND.
6. - THIRD EXPERIMENT: EXAMINATION OF A ROCKER
D
It is often necessary to memorize the logical state H or L of a signal at one moment given thanks to a control signal.
In this case, one uses a rocker D, of type MM 74C74 whose electric diagram is given figure 12.
This integrated circuit, as you can see it, includes/understands two rockers of the type D identical, of which only one will be examined.
As you can observe it in figure 12, each rocker D has the four following entries :
DATED : English
term meaning “given” whose initial D
gives the name to the rocker.
CLOCK : English
term meaning “clock” ; it corresponds to
the entry of order (entered C of the rocker
relating to the preceding experiment).
CLEAR
PRESET
You will see the function of these two last entries during the experiment.
In each of the two rockers D,
one lays out of two noted exits Q and
which are complementary one of the other.
Begin handling by conforming you to the following indications :
a) Disconnect the food and remove all the connections carried out during the last experiment.
b) Remove the integrated circuit MM 74C00 of support ICX and introduce into this last the integrated circuit MM 74C74.
c) Carry out connections visible on the figure 13-a and enumerated below :
stitch 1
of support ICX with the P0
contact 
stitch 2 of support ICX with contact SW0
stitch 3 of support ICX with contact SW1
stitch 4
of support ICX with the P1
contact
stitch 5 of support ICX with the L0 contact
stitch 6 of support ICX with the L1 contact
d) Put SW0 and SW1 on position 0. With the connections carried out, you carried out the illustrated circuit appears 13-b.
e) Connect the food and observe the LED L0 and L1 : one of both is lit and the other is extinct; with the powering, the rocker positions either in a high state, or at the low state, without one being able to envisage which.
You will examine the functions of the entries now DATED and CLOCK, two entries CLEAR and PRESET not being taken into account for the moment.
f) Lay out SW1
on position 1, thus bringing entry CLOCK
to the level H. You note that the LED
L0 is extinct, while L1 is lit.
This indicates that the exit Q of the rocker
went, if it were not it already at the time of the connection of the food, to
state 0. The exit Q
is thus on the level L and
the level H.
g) Now give SW1 on position 0 and place SW0 on position 1: by observing the LED, you note that the exits did not change a state.
h) Again lay out SW1 on position 1 : you observe that L0 ignites immediately. This indicates that the rocker was put at state 1. It memorized the fact that on the entry a level H (i.e. a logical level 1) DATED is applied.
i) Carry out several times the same operations, i.e. rock switch SW1 of position 0 with position 1 for the two positions of SW0.
You observe that each time SW1 passes from position 0 to position 1 (i.e. of state 0 with state 1), the rocker is put at the same state that that of the entry DATED. Remember that the state of the rocker is defined by the state of the exit Q and statement that the rocker is with state 1 is equivalent saying that Q is with state 1 or is with the state H.
The rocker takes into account the level applied to entered DATED at the time when the commutation of SW1 of state 0 with state 1 occurs.
j) Leave SW1 on position 1 and commutate SW0 on several occasions. You note that the state of the rocker indicated by L0 and L1 does not change. You thus have just seen that the rocker is sensitive to the level of the entry DATED only at the moment when entry CLOCK passes from the level L on the level H.
This is the fundamental characteristic of rocker D. It has an entry of order as rocker R.S.C seen in the preceding experiment, but commutates only at the time of the positive transition from the level applied to the entry of order, and not on a given level applied to this entry. The entry of the rocker is thus validated only during very short time where the level of tension of entry CLOCK passes from the level L on the level H.
On the other hand, in rocker R.S.C., the entries are validated during all the time where the order is on the level H.
Entry CLOCK is very important in the digital circuits, because it allows to make them function in synchronism, i.e. the changes of state of the exits are carried out at the rate/rhythm imposed by the clock.
In the next practices, function CLOCK will be explained. For the moment, consider it simply as an entry of order validating the rocker.
Now let us see the functions of two remaining entries CLEAR and PRESET which were not taken yet into account.
k) Press on the P0 button, which makes it possible to apply an impulse to entry CLEAR. You observe that L0 dies out and that L1 ignites, independently of entry CLOCK, which wants to say that the rocker is forced with state 0.
l) Press now on the button P1, you thus send an impulse to entry PRESET. You observe that L0 ignites while L1 dies out. The rocker is forced with state 1.
With these two tests, you obtained the practical confirmation of the function of entries CLEAR and PRESET which, independently of the entry of order CLOCK, force the rocker with one or the other of the two possible states at exit.
Term PRESET means “to predispose”, therefore this entry makes it possible to predispose the rocker with state 1.
Term CLEAR means “to erase”, therefore this entry makes it possible, as you noted, to erase a possible logical state 1 at exit of the rocker. It gives to 0 the exit of the rocker.
m) Finally try simultaneously to bring to the level L two entries CLEAR and PRESET while pressing at the same time on the two buttons P0 and P1.
You note that the exits Q
and
pass both on the level L, while by
slackening the buttons then, the rocker is put in a state which cannot be given
in advance. This configuration of the two entries is not thus of any practical
utility, just like in rocker R.S., where the
configuration of the entries 
= 0 and 
= 0 was not it more.
On the basis of result obtained with the tests carried out, you can draw up the table of operation and draw from this one the truth table of the rocker D deferred on figure 14.
The table of operation summarizes all the results of the experiment. The arrows directed upwards in the column of entry CLOCK represent a positive transition which is the passage of the level L on the level H of the signal applied to this entry.
You also point out that symbol X means that the entry to which it refers, can be indifferently on the level L or H without influencing the state of the rocker with the conditions specified for the other entries.
Made experiment and observation of the tables of figure 14, one can summarize thus the operation of the rocker D:
the circuit memorizes the state of the entry DATED
at the time from the transition from the level L
to the level H from the signal applied to
entry CLOCK.
entries PRESET
and CLEAR are not validated by entry CLOCK.
They are used respectively to position the circuit with state 1
or state 0.
This is very useful, when the food is connected, for example to put the rocker at the wished state, instead of him to let take an unspecified state.
7. - FOURTH EXPERIMENT : USE
OF A “ROCKER D” LIKE DETECTOR OF POSITIVE TRANSITIONS
In this experiment, you will check how it is possible to exploit the characteristics of the rocker of the type D by adding to the digilab that you are building another circuit which will be particularly useful for the later experiments.
a) Disconnect the food, remove the integrated circuit MM 74C74 of support ICX and introduce it into support IC3.
Via the tracks of the printed circuit, the various pins of the integrated circuit are connected to the various contacts of the group of connectors as represented by the diagram of figure 15.
Indeed, as you can see it, the entries CLEAR, CLOCK and the exit Q of the first rocker are connected respectively to the contacts located by symbols CL1, CK1 and OUT1 of the group of connectors, while the same entries and exits of the second rocker are connected to contacts CL2, CK2 and OUT2.
Entries PRESET
and DATED are connected to the tension +
V and are thus permanently on the level H,
while the exit
is not connected.
One connects entry PRESET to the level H so that it does not have an influence on the operation of the rocker.
The exit
is not connected since it is not used.
b) Carry out now the connections between the various contacts of the group of connectors represented figure 16-a as enumerated below :
CK1 with SW0
CK2 with SW1
CL1
with P0
CL2
with P1
OUT1 with L0
OUT2 with L1
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In a this way SW0
and connected to entry CLOCK of the first
rocker, the exit Q with the LED
L0 and entry CLEAR with the P0
push-button.
The second rocker is connected in a
way similar to switch SW1, the
LED L1 and the P1
push-button.
Carry out the following operations now :
c) Connect the food and put SW0 and SW1 on position 0.
d) Press on the button P0, you thus apply a negative impulse to entry CLEAR of the first rocker. You note that L0 dies out, therefore that the rocker passes to state 0.
In this way, the circuit is preposition or initialized, i.e. it was put in a state known and wished so as to be able to continue the experiment starting from a state well defined and chosen, in fact state 0.
e) Now put SW0 on position 1. L0 ignites immediately. Indeed, to entry CLOCK is applied a transition from the level L to the level H, the rocker thus takes the state determined by the entry DATED.
Since the latter is on the level H, the rocker passes to the state corresponding, i.e. on the level H thus causing the lighting of L0.
If the test did not provide the results envisaged, re-examine with more attention the connections and made a meticulous visual monitoring of the tracks of the printed circuit connecting support IC3 and the contacts of the group of connectors. Also remade weldings.
f) Give SW0 on position 0 and press then on the P0 push-button. The LED dies out.
g) Try to make rock several times SW0 of position 0 with position 1 and vice versa.
With each transition from state 0 to state 1 realized in this way, you note that L0 ignites if it is not already lit. The P0 push-button makes it possible to extinguish it.
h) Repeat the same operations on the second rocker by actuating SW1 and the P1 push-button and by observing the LED L1.
At the end of handling, leave the integrated circuit MM 74C74 permanently inserted in support IC3.
You thus tried out a circuit which detects the transitions from the level L to the level H : it will be shown particularly useful to detect too short impulses to be visualized by means of the LED. One can say that the circuit memorizes the impulses while being put at state 1 and remains in this state even after the disappearance of the impulse whose it announces the existence.
In the next practice, you will examine other types of circuit and you will continue the experiments with increasingly complex circuits.
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