The
meters prépositionnables |
Meters
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Created it, 06/09/09
Update it, 06/09/23
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5. - REVERSIBLE COUNTERS
Up to now you saw meters which increment of a unit their contents with each fresh impulse.
There are also meters which décrémentent their contents. One speaks then about discounting machines.
The diagram of figure 41 is a discounting machine of module 8 carried out with 3 rockers D. the chronogram relating to its operation and the diagram of the states is also represented in this figure. We can compare this diagram with that of figure 12.
The first rocker is always cabled out of divider by two since the LSB passes alternatively from “0” to “1” in counting mode as in countdown mode.
On the other hand, for the two following rockers, it is the exit
Q of the preceding rockers which provides
the clock signal and not 
.
Figure 42 represents the diagram of a synchronous discounting machine of module 8.
A combinative network composed of three doors is here necessary.
The discounting machines exist in the form of integrated circuits. These circuits function either in counting mode, or in countdown mode. There are two types.
In the first type, there is only one entry of ordering of the counting mode/countdown.
In the second type, there are two entries of clock; one relates to the mode counting, the other with the countdown mode.
Figure 43 represents these two possibilities.
An example of meter/integrated discounting machine (4029) will be presented at the chapter 6. 2.
6. - METERS
PRÉPOSITIONNABLES
6. 1. - PRINCIPLE
On the market of the components, it is easy to find meters of module 2n or 10 (in general, n ³ 4).
On the other hand, for a meter having n states (n odd), it is necessary to resort to a combinative network, which increases the complexity of the circuit.
For this reason the manufacturers developed meters prépositionnables.
The latter make it possible to limit the number of the states which a meter can take, in other words, they make it possible to reduce the module.
For a meter prépositionnable whose maximum module is 16, it will be possible to reduce this module between 2 and 16.
For that, these meters have as many entries of presetting exits. The diagram of figure 44 represents such a meter.
The four entries I1, I2, I3 and I4 are the entries of presetting.
CARRY is an exit of reserve or carryforward. This exit is on the level H only when the four exits Q1, Q2, Q3 and Q4 are on the level H. Autrement, it remains on the level L.
Entry LOAD is an entry of order. It makes it possible “to charge” the meter in the logical state where the four entries of presetting are.
If the loading is asynchronous, as soon as entry LOAD is on the level L, the logical state of I1 is transmitted to Q1, that of I2 with Q2 and so on…
If the loading is synchronous, it is necessary first of all that entry LOAD is on the level L (active level), then it is necessary to apply a clock pulse so that the loading is carried out.
By carrying out the wiring of figure 45, it is possible to use the exit CARRY for prépositionner the meter.
When the meter passes to state 15, entry LOAD passes on the level L and the loading is carried out with the face of clock which will follow (entered synchronous LOAD).
The chronogram of figure 46 shows an example of operation with this assembly.
The meter is prépositionné with state 13 and its module is 3 (States 13, 14 and 15).
With this type of assembly, it is possible to pass from a state predetermined (here 13) to the state a 15 (in the case of meter modulo 16), but this meter does not pass by states 0, 1, 2…
If one wants to begin the phase of counting from 0, it is necessary to carry out one of the two assemblies of figure 47.
In the figure 47-a, when the exit of the meter passes to 01012 = 510, entry LOAD passes to state 0. Therefore, with the next clock signal, the meter passes by again with state 0 since the four entries of presetting are cabled with the mass (entered synchronous LOAD).
It is also possible to use entry CLEAR as indicated in the figure 47-b ; this entry CLEAR being also synchronous.
In both cases, door NAND is used to detect state 5 of the meter so that it passes by again to 0.
Nevertheless, this system is too rigid because it imposes a combinative network given to produce a meter of definite module. However, with a meter prépositionnable, it is enough to change the data on the entries of presetting to modify the module.
6. 2. - THE METER INTEGRATED HEF 4029B
It is a meter/binary/decimal synchronous discounting machine 4 bits produced in technology MOS.
Its functional diagram and its stitching are given on figure 48.
The clock signal is applied to the
entry CP. In fact the rising faces are
active. 
is an entry of validation. If it is on the level H,
the meter is inhibited as well as reserve. PL
is the entry of asynchronous parallel loading priority. As soon as it passes on
the level H, the four data present on P0,
P1, P2 and P3 are transferred on
the exits O0, O1, O2 and O3.
Order UP / 
makes it possible either to count (UP /
on the level H), or to deduct (UP
/
on the level L).
Order BIN /
allows counting/countdown either in binary code (BIN
/
on the level H), or in decimal
code (BIN /
on the level L).
The exit 
is normally on the level H and passes on the
level L when the meter reaches the maximum
account in counting mode or the minimal account in countdown mode provided that
is on the level L.
We will see in the chapter according to the use which is made of
this exit .
The table of figure 49 presents the various operating modes from this meter.
| PL | BIN
/
|
UP
/ |
|
CP | MODE |
| H | X | X | X | X |
Parallel loading |
| L | X | X | H | X | Without change |
| L | L | L | L |  |
decimal countdown |
| L | L | H | L | |
Decimal counting |
| L | H | L | L | |
Binary countdown |
| L | H | H | L | |
Binary counting |
All in all, there are four operating
modes since there are two entries of order (BIN /
and UP / )
authorizing four combinations.
The diagrams of the states of figures 50 and 51 represent these four operating modes.
In figure 50, you can notice that if the meter is in a state ranging between 10 and 15 (case of the powering), it reinstates the ring of the states after a certain pulse repetition frequency of clock. For example from state 12, it passes to state 13 then to state 4 in counting mode.
The chronogram of figure 52 illustrates the operation of this
meter in decimal mode. Entry BIN /
is on the level L.
At moment t1, order PL (loading of the meter) Thus passes on the level L. to the active face of clock which follows, counting can start.
is with the state “0”. Counting is
validated. The meter thus increases by “0”
to “9”. As soon as it passes to “9”
at the moment t2, the exit
(retained) passes on the level L.
During this state 9, the
entry of order UP /
places on the level L, therefore
the meter will pass in countdown mode. Immediately, the exit
passes by again on the level H since the
meter is in countdown mode. To the active face of clock according to, the meter
passes to 8 then to 7…
up to 0.
At moment t3, the
discounting machine passes to “0” but
the exit
remains on the level H since the entry of
validation
has just passed on the level H.
On the other hand, after one period of the clock signal, this
entry
passes on the level L and consequently the
exit
can pass on the level L.
At the moment t4, order PL thus places on the level H the loading of the meter is carried out and this last passes to the state “6”.
It would be possible to trace the same type of chronogram for the binary mode.
7. - METERS OF
GREAT
CAPACITY
7. 1. - MEETING OF SEVERAL METERS IN CASCADE
We can make two note :
First of all by using individualized rockers, we are very quickly limited to the
level of the capacity of such a meter.
Indeed, it becomes necessary to use a significant number of integrated circuits (rockers and combinative network).
Then, the meters existing in the form of integrated circuits hardly exceed a
dozen stages (standard 4040), therefore
limit the capacity to 4095 = 212 - 1.
There are integrated meters having to 24 stages (case of circuit 4521) but all the stages do not have an exit. These circuits are generally used as dividers and not like meters.
Therefore one joins together several meters together as schematized on figure 53.
It is enough to connect the Q4 exit of a meter (synchronous or asynchronous) of row N to the entry of clock of the following meter (of row N + 1). One intercalates a reverser between this exit Q4 and the entry of clock because this one is active on the face going up (in this case).
If each meter has a module equal to 16 (divider by 16), the total module is equal to 16N, if N is the total number of meters.
On the Q4 exit of the Nth meter, one can collect a signal of frequency:
Frequency of clock / 16N
For two meters in series, the module is worth 256 (16 x 16) and the clock signal is divided by 256.
Certain meters have an exit CARRY (retained) and two entries of validation of the meter (for example, CEP and CET).
If these two entries pass on the level L, the meter is blocked in the state where it is at this time.
These characteristics make it possible to carry out the assembly of figure 54.
When the meter N° 1 reached its maximum capacity, the exit CARRY passes on the level H and consequently, with the active face of the clock which will follow, the meter N° 2 is incremented (case of a meter) and the meter N° 1 will pass to the state “0”. This moment, the exit CARRY passes by again on the level L, which invalidates the meter N° 2 again.
The meter N° 3 is incremented only if the exits CARRY of the first two meters are on the level H. this moment, the entry CEP of the meter N° 3 passes by again on the level L, which invalidates it again and so on…
It should be noted that the exit CARRY passes on the level H only if the meter reached its maximum capacity and if its entry CET is on the level H.
Thus, one is certain that a meter of row N will be incremented only if all the meters which it preceding reached their maximum capacity.
With the meters / discounting machines having two entries of clock (for the counting mode, the other for the countdown mode), an exit CARRY and an exit BORROW, it is possible to carry out the assembly of figure 55.
Entry UP is the entry of counting and entry DOWN that of countdown.
In counting mode, operation is identical to that of the assembly of figure 53.
In this case, the exit CARRY is active to 0. When the meter N° 1 is with state 15, the exit CARRY is on the level L. With the face of clock according to, it passes by again on the level H and allows the incrementing of the meter N° 2. The operation of the unit is asynchronous.
In countdown mode, exit BORROW (retained countdown) passes on the level L when the discounting machine reaches state 0.
Therefore, when a new active face arises on entry DOWN of the meter N° 1, this last passes by again at state 15 and exit BORROW with the state “1”, which décrémente of a unit the meter N° 2.
7. 2. - EXAMPLE OF REALIZATION OF A METER OF GREAT CAPACITY WITH THE METER INTEGRATED HEF 4029 B
By connecting several meters HEF 4029 B as indicated in figure 56, it is possible to obtain a meter / discounting machine of great capacity.
The entry of validation
of the first meter is cabled with the mass permanently.
Then, the exit
of each meter is connected to the entry
of the following meter. Therefore, so that a stage (a meter HEF
4029 B) of row N can be
incremented (décrémenter), it is necessary that its entry
is on the level L, therefore that the meter
of row N - 1 reached its maximum capacity
(in this case, the exit
passes on the level L).
In addition, so that the exit
of the meter of row N - 1 is on the level L,
it is necessary also that its entry
is on the level L.
Consequently, so that a meter of row N can be incremented (décrémenter), it is necessary that all the meters which precede it reached their maximum capacity.
With this assembly this theory is completed on the meters.
The following theory will introduce the systems of decoding and the bill-posters to you.
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