Created it, 06/10/19
Update it, 06/10/31
N° Visitors
2. - PREPARATION OF THE MATERIAL
To carry out the experiments envisaged in this practice, it will be necessary for you to use the following material :
1 integrated circuit MM 74C163
1 integrated circuit MM 74C193
1 integrated circuit MM 74C02
1 integrated circuit HM 6116P-4
1 integrated circuit 74LS245
1 integrated circuit CD4040
3. - FIRST EXPERIMENT : EXAMINATION AND OPERATIONAL TEST OF A BIDIRECTIONAL BUFFER THREE STATES.
In this experiment, the integrated circuit 74LS245 will be used, it contains eight bidirectional buffers TRI-STATE, as represented in the diagram of figure 14.
.gif)
At boundaries 2, 3, 4, 5, 6, 7, 8 and 9 can be connected eight lines of A1 to A8, and eight others can be connected to pins 18, 17, 16, 15, 14, 13, 12 and 11 of B1 with B8.
The data can be transmitted of A
towards B or B
towards A depending on the state of the
order applied to pin “DIR” (abbreviation
of direction) when the entry of order ENABLE
is on the bottom grade.
When entry ENABLE
is at the high level, the passage of the data is interdict in the two
directions, because all the buffers intern with the integrated circuit are with
the state “high impedance”, which is
equivalent saying that the exits of those are disconnected from the bus.
You can notice the sign represented inside each buffer ; it indicates that the buffers used comprise a circuit of re-arrangement of the trigger type of Schmitt.
You can see figure 15, the internal configuration of the circuit for only one of eight ways A towards B or vice versa; we will use this diagram thereafter to include/understand the circuit and to draw up of it the table of operation during the experiment.
Will finally know that the circuit 74LS245 is a circuit of technology T.T.L and that, for this reason, it must be fed with a stable tension of 5 V. A higher tension could damage it.
3. 1. - REALIZATION OF THE CIRCUIT
a) Remove matrix with contacts all the connections and the components relating to the last experiment.
b) You of the good position of the on / off switch of Digilab ensure. It must be in position OFF at the time of its connection on the sector.
c) Insert the integrated circuit 74LS245 on the matrix, in the position indicated to the figure 16-a. Carry out then the connections necessary.
.gif)
The figure 16-b represents the diagram of the electric circuit carried out.
3. 2. - OPERATIONAL TEST
In this first phase, you will check the operation of the one of the eight bidirectional buffers of the integrated circuit.
a) Put SW1 on position 0 to validate the circuit and put SW0 on position 1.
b) Energize Digilab : L0 and L1 flicker then at the rate of 10 Hz. Indeed, when SW0 is in position 1, the passage of the signal in the direction of A8 with B8 is authorized. This is due to the fact that the exit of door 2 of figure 15 is at the high level whereas that of door 1 is on the bottom grade thus prohibiting the B8 direction towards A8.
c) Put SW1 on position 1 ; in this way, the two ways are cut and the signal does not pass in any of the two directions.
Indeed, L0 still flickers, ordered by the signal coming from CP1 ; on the other hand L1 does not flicker any more. It presents a luminosity weaker than the normal.
d) Without changing the other connections, connect the B8 exit of the buffer (pin 11) with + : L1 ignites with its full intensity.
e) Connect the B8 exit with the mass : L1 dies out. You thus noted that L1 can be ordered independently of the buffer which, not validated, does not intervene.
f) Remove the connection between pin 11 of the buffer and the mass.
g) Extinguish Digilab.
Now reverse the direction of transmission by applying the rectangular signal provided by CP1 to the B8 entry. Observe what occurs on A8.
h) For that, remove the connection between pin 9 and contact CP1, then connect pin 11 and contact CP1. Rock then SW1 on position 0 to validate the circuit again.
i) Place SW0 on position 0, you thus reverse the direction of transmission compared to the preceding test.
j) Light Digilab ; you see that L1 and L0 flicker both, the signal passes indeed from B8 towards A8. To check if the signal goes indeed from B8 towards A8, repeat the same procedure as for the preceding case.
k) Put SW1 on position 1 : the two ways are stopped, L1 flickers, while L0 remains lit.
l) Connect L0 with + ; you note that it ignites.
m) Put L0 at the mass ; it dies out.
You have just checked the two directions of transmission of the signal between A8 and B8 of the one of the eight ways of the integrated circuit. Adopt the same procedure for the seven other ways in order to check correct operation.
n) Extinguish Digilab.
By basing you on the results obtained, you can build the table of operation of the bidirectional buffer indicated figure 17 which can be summarized schematically by figure 18.
4. - SECOND EXPERIMENT : OPERATIONAL
TEST OF A METER A TWELVE STAGES.
To carry out the following experiments, it will be necessary to use a meter. In the preceding practices, you tried out various types of meters; that that you will examine now is not different from the others as for its design, but it has the great advantage of containing 12 stages in a single integrated circuit.
It is about the CD4040, binary asynchronous meter with 12 bits, whose synoptic diagram is represented figure 19. The stitching of this circuit is indicated on figure 20.
The impulses to be counted must be applied to the entry located by f1, which is connected to a door NAND ordered by the entry RESET.
The door of entry NAND is followed of a trigger of Schmitt who is used to improve quality of the signal, then come two reversers which control the chain of dividers.
The meter is incremented each time the entry f1 passes from the high level on the bottom grade, i.e. with each downward face. This is symbolized by a bubble placed on the entry f1 in figure 20.
The entry RESET gives the meter to zero, it is asynchronous ; as soon as a level H is applied to him, the meter passes to 0.
The meter can go from 0 to 4095 (212 positions). On the exits, one obtains the binary number by applying positive logical convention (level L = 0 ; level H = 1).
4. 1. - REALIZATION OF THE CIRCUIT
a) Remove matrix the connections and the components relating to the preceding experiment.
b) Insert on the matrix the integrated circuit CD4040 in the position indicated to the figure 21-a and carry out the connections.
.gif)
The electric diagram of the circuit carried out is represented figure 21-b, while the figure 21-c represents its synoptic diagram.
4. 2. - OPERATIONAL TEST
a) Put SW0 on position 1.
b) Connect the food : you observe that the LED of L0 with L3 are extinct and that the two bill-posters indicate figures 00.
c) Put SW0 on position 0 : you note that the meter is released and started to count from 0.
On the twelve exits of Q1 with Q12, one finds a number binary of twelve bits active of :
The most significant bit (M.S.B.) corresponds to the Q12 exit and the least significant bit (L.S.B.) at the Q1 exit.
With the LED L0 in L3, one visualizes the bits of Q1 with Q4, with DIS 0, one can visualize the bits of Q5 with Q8 and with DIS 1, one visualizes those of Q9 with Q12.
Observe the LED and the bill-posters ; since the clock is at the frequency of 10 Hz, the LED L0 flickers at the frequency of 5 Hz, L1 at the frequency of 2,5 Hz, L2 with 1,25 Hz, L3 with 0,625 Hz.
After the sixteenth clock pulse, the incrementing of the indication of the bill-posters starts, this one being in hexadecimal code, of 00 to finish to FF at the end of counting.
By observing the LED and the bill-posters, check the correct operation of the meter by consulting the table of figure 22. To figure 0 of the column will have to correspond the extinct LED and to figure 1, the lit LED.
Of course, it is not a question to hope the clock pulses up to 4095 to check the table : it is enough to observe that the LED and the bill-posters follow the sequence indicated in the table.
d) After having finished the test, extinguish Digilab.
By commenting on the experiment, one can say that each stage of the meter carries out a division by two of the frequency of the signal applied to its entry ; if one injects the signal with 10 Hz, coming from contact CP1, at the entry f1 of the meter, the various exits, one obtains signals whose frequency is each time reduced by half. This can be easily checked, by observing the rate/rhythm to which the LED flicker and to which the bill-posters increment themselves. The table of figure 23 indicates the frequency and the period of the signals of the various stages of the meter and summarizes the test results.
| Exit | Pin | Frequency (Hz) | Period (s) |
| Q1 | 9 | 5 | 0,2 |
| Q2 | 7 | 2,5 | 0,4 |
| Q3 | 6 | 1,25 | 0,8 |
| Q4 | 5 | 0,625 | 1,6 |
| Q5 | 3 | 0,3125 | 3,2 |
| Q6 | 2 | 0,15625 | 6,4 |
| Q7 | 4 | 0,078125 | 12,8 |
| Q8 | 13 | 0,0390625 | 25,6 |
| Q9 | 12 | 0,0195313 | 51,2 |
| Q10 | 14 | 0,0097656 | 102,4 |
| Q11 | 15 | 0,0048828 | 204,8 |
| Q12 | 1 | 0,0024414 | 409,6 |
As you can note it, the frequencies spread out of 5 Hz with 0,0024414 Hz, i.e. an extremely low frequency. It is thus enough to a little attention to observe the phenomenon and if there would remain some points obscure, do not hesitate to start again several times the experiment.
Click
here for the following lesson or in the synopsis envisaged to this end. |
High
of page |
 Preceding
page |
Following
page |
