Created it, 06/10/19
Update it, 06/11/01
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8. - SIXTH EXPERIMENT: USE OF THE MEMORY TO GENERATE SEQUENCES
One often sees neon signs on which the inscriptions move, ignite and die out according to a programmed sequence. The circuits making it possible to obtain that are numerous and you already saw of them one in the theory devoted to the registers with shift. In this experiment, you will use the memory to achieve the same work in a manner more flexible easily programmable bus.
8. 1. - REALIZATION OF THE ASSEMBLY
a) Remove connections between the entries of the buffer 74LS245 (pins 2, 3, 4, 5, 6, 7, 8, 9) and as well as the connection in dotted line represented figure 41 masses it, without changing however the other connections. You ensure that pin 21 of memory HM6116P-4 are well connected to SW0 and not to pin 10 of meter CD4040.
b) Insert integrated circuits MM74C163 (binary counter synchronous of module 16) and MM74C193 (synchronous decimal scaler) in the positions indicated on figure 41.
Carry out then the connections.
Figures 42 and 43 respectively represent the electric diagram and the synoptic diagram of the circuit which you have just carried out.
As you can note it, two meters were added ; they are put in cascade and form a meter with 8 bits. The clock signal which orders this meter comes from contact CP1. The P1 button validates when it is inserted the shunting of CP1 through an NOR door.
The two meters are used to compose the data to write in a way more convenient than with the system used previously.
It is enough to insert P1 so that the meters are incremented in a more or less fast way, according to the frequency of the clock signal, until the exits of those give the wanted value, which is written then in the memory by the usual procedure.
Moreover, the meter of addresses was modified so as to count in module 64. This is obtained by connecting the Q7 exit with the RESET so that when number 64 (1 000 000 in binary code) is reached, the meter totals 0.
The accessible positions memories in which one can read and write data of 8 bits, are thus 64.
8. 2. - OPERATIONAL TEST
It is a question of writing in memory data such as, read after, they make it possible to light the LED according to a pre-established program. To do that, it is enough to proceed in the following order :
Prépositionner memory.
To prepare the data.
To write the data with the prepared address.
To increment the address of a step.
To prepare the new data.
To write the new data.
Proceed in the same way to the last address available, i.e. 64 since to the blow of clock according to, the meter of address totals zero.
To write the data in memory, it is necessary to achieve the operations enumerated below :
One forms the address
while supporting on P0 up to the value of
the desired address. This one is read on bill-posters DIS0
and DIS1.
One prepares the data
by inserting P1 until the LED
visualize the desired value of the data.
One writes the data
by rocking SW0 of position 1
with position 0 and while giving it then
again on 1.
Proceed in the following way :
a) Put SW0 on position 1.
b) Put SW1 on position 1 (you inhibit the exit of the memory).
c) Put SW2 on position 0 (you validate the memory).
d) Light Digilab.
e) Write in memory the data indicated to the table of figure 44.
In the first two columns of this table the address is deferred such as it appears on DIS0 and DIS1 ; in the third column the hexadecimal value of the data is indicated and in the eight other columns, the value of the data such as it is read on the LED (“NOT” indicates that the corresponding LED are extinct, while the empty boxes mean that the corresponding LED are lit).
Check now if the data are well written in memory.
f) Put SW0 on position 1, you authorize the reading thus.
g) Put SW1 on position 0 : the exit of the data is validated. Leave SW2 on position 0.
h) Position the meter of addresses to address 00.
i) Examine the LED : they must all be lit, except L7, as the first line of the table of figure 44 indicates it.
j) Continue the reading of the data, the address is incremented step by step.
k) Check the exactitude of the data by maintaining P0 inserted : the LED flicker according to the programmed sequence. This continuous sequence to be held as long as you do not slacken the button.
If you wish to increase speed, it is enough to change the frequency of the clock signal while passing from 1 Hz with 10 Hz.
l) At the end of the experiment, extinguish Digilab.
You point out that by disconnecting the food, all the data written in the memory are lost.
In this handling, you carried out a sequential system with programmed logic recorded in a memory.
This type of application is particularly important because the LED can be replaced by various control circuits such as actuating relay of the machine tools, or to carry out any system whose operation must be ordered in a sequential way.
Currently, the microprocessors are largely used for these orders, but that is not worth always the sorrow to invest money and to waste time for the development of a project with microprocessor. In such cases, a control circuit to recorded sequences is the most advantageous solution.
The volatile memories, of the type of those which you used in the experiments of this practice 12, are used only when it is necessary to change sequences quasi continuously. So on the other hand, the sequence is always the same one or only is very seldom changed, it is advisable to use said nonvolatile memories memories died such as the ROM or the EPROM.
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