Pulse or digital communications – Receivers – Particular pulse demodulator or detector
Reexamination Certificate
1999-01-12
2004-08-03
Corrielus, Jean B. (Department: 2631)
Pulse or digital communications
Receivers
Particular pulse demodulator or detector
C375S369000
Reexamination Certificate
active
06771716
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method of communication, and, more particularly, to a method of digital communication between a master unit and a slave unit.
BACKGROUND OF THE INVENTION
Digital transmissions, such as between a master and a slave, can be made over different media. The transmission channels may be wire links or optical fibers or the space between two antennas.
FIG. 1
shows an exemplary communication using RF links. In this figure, a master unit
1
uses a transceiver antenna
11
to exchange messages with a slave unit
2
also equipped with a transceiver antenna
22
. The transmission channel is through air between the two antennas
11
and
22
.
The master unit and the slave unit may each either transmit messages to the other unit or receive messages from the other unit. The master unit is distinguished from the slave unit in that it is the master unit that takes the initiative in the communication. The master unit may thus be, for example, the central processing unit of a computer. The slave unit may then be one of its peripherals, such as, a printer that is remote-controlled by any transmission channel.
In the prior art, there are known methods of communication including the transmission of messages comprising a useful information word and one or more service bits. The transmission is carried out serially according to a specified communications protocol. A protocol of this kind specifies the format and the syntax of the messages that are transmitted by the master unit to the slave unit or vice versa. The transmission is done synchronously. It is sequenced at a specified rate, the units using known approaches to lock in to the rate of one and the same clock or two synchronous or bi-synchronous clocks.
FIG. 2
shows a fairly simple example of a known message format. The message comprises first of all a starting bit START whose function is to synchronize the clock of the addressee unit with the received message. Then, the message comprises a useful information word INFO that is encoded, for example, on eight bits (one byte). This word may be an instruction word whose value indicates the nature of a command to be carried out by the addressee unit. This instruction may, for example, be a read or write command. It may also be an address word whose value indicates the address or a part of the address of a memory location of the addressee unit. At this memory location of the addressee unit, a data element may, for example, be read or written. Finally, it may also be a data word whose value indicates the value of a data element processed by the addressee unit.
The message also comprises a check bit CHECK which, in particular, may be a parity check bit. The value of the parity check bit CHECK is fixed at the logic value 1 or 0. This value is determined in such a way that the sum of the values of the bits of the useful information INFO gives an even value or an odd value depending on the type of parity chosen. The role of the parity check bit CHECK is to enable the addressee unit to detect transmission errors if any. In such a case, the addressee unit may, as the case may be, request a retransmission of the message.
Finally, in the prior art, the message comprises an end-of-transmission bit STOP. This bit is used solely to indicate the end of the message. Following this end-of-transmission bit STOP, each protocol generally provides for a number of elementary timing intervals during which a transmission unit no longer transmits any bit on the channel. Thus, the channel is left free so that the addressee unit sends a bit with a specified logic value for the acknowledgment of the communication. The logic value of this acknowledgment bit indicates whether the message has been accurately received.
The basic approach used in the prior art to determine whether the message has been accurately received is the check performed by the parity check bit CHECK. Furthermore, depending on the protocol used, a specified value of the acknowledgment bit prompts a retransmission of the message in the event of incorrect reception. In
FIG. 2
, four of these elementary timing intervals following the bit STOP have been shown.
In electronic systems, there are a very large number of different communication protocols. Each protocol is suited to specific constraints of a given application. These constraints may be the size of the words to be transmitted, the need to secure communications against passive or active intervention by ill-intentioned individuals, constraints related to an acknowledgment mode, maximum duration of transmission in relation to the bit rate, etc. Within such a system, the master unit and the slave unit conform to a common communications protocol so that they can communicate with each other intelligibly.
In general, the information on the communications protocols developed by electronics systems manufacturers is widely disseminated. These manufacturers thus enable other manufacturers to incorporate these systems into more complex assemblies or develop new industrial and/or commercial applications thereof.
The result thereof, with respect to the size of the communications in which such protocols are used, is that the integrity of the information transmitted has to be optimum. In other words, it is necessary for the transmission to be affected by a minimum of errors. Furthermore there are applications where the integrity of the information exchanged is a major constraint in the specifications. In the prior art, the control of the quality of the transmission of the binary signals lies basically in the analysis and interpretation of the value of the parity check bit CHECK mentioned above.
Unfortunately, this check is not completely reliable. In particular, it proves to be valid only when an odd number of bits has been transmitted erroneously. Indeed, even numbers of errors are likely to compensate for one another with respect to the parity check bit.
FIGS. 3A
,
3
B and
3
C show three cases of possible transmission. For these examples, the message format of the kind shown in
FIG. 2
has been kept. No special attention has been paid in these figures, to the value of the starting bit START and end-of-transmission bit STOP. All that has been taken into account here is the values of the useful information word bit INFO and the parity check bit CHECK.
FIG. 3A
shows the case of a useful information bit INFO
1
received without transmission errors. It has been chosen arbitrarily to give the logic value 1 to seven first bits B
1
, B
2
, B
3
, B
4
, B
5
, B
6
, B
7
of the useful information word INFO
1
. A last it B
8
of the useful information word INFO
1
is set at the logic value 0. If it is chosen to adopt a so-called even type of parity, the parity check bit CHECK will then take the logic value 1. In the case of
FIG. 3A
, the transmission of the useful information word INFO
1
is not affected by errors. A useful information word INFO
2
which is the word resulting from the transmission of the useful information word INFO
1
consequently has the same binary values for each of the bits.
In general, a circuit formed by elementary logic gates is used to ascertain that the result of the transmission of the useful word is in accordance with the result expected with regard to the value of the parity check bit and depending on the type of parity adopted.
FIG. 3B
shows the case of the same useful information word INFO
1
received with a transmission error. A useful information word INFO
3
is received in the reception unit following the transmission of the useful information word INFO
1
. In
FIG. 3B
, the eighth bit B
8
of the useful information word INFO
3
is different from the eighth bit of the useful information word INFO
1
. The transmission has therefore been erroneous and the useful information word INFO
3
is then no longer matched with the parity check bit CHECK. It would have been the same if three, five or seven of the eight bits constituting the useful information word INFO
3
had been different from the bits of the useful information word IN
Allen Dyer Doppelt Milbrath & Gilchrist, P.A.
Corrielus Jean B.
Jorgenson Lisa K.
STMicroelectronics S.A.
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