Error detection/correction and fault detection/recovery – Pulse or data error handling – Digital data error correction
Reexamination Certificate
2002-03-14
2003-11-11
Ohung, Phung M. (Department: 2133)
Error detection/correction and fault detection/recovery
Pulse or data error handling
Digital data error correction
C714S807000
Reexamination Certificate
active
06647527
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to digital transmission, and more specifically to an efficient method for communicating between master and slave units by using a protocol having improved acknowledgment during message reception.
2. Description of Related Art
Digital transmissions can be made by means of different media. The transmission channels may indeed be either wire links, optical fibers, or a volume of air between two antennas.
FIG. 1
shows an example of communication using RF links. As shown, a master unit
1
uses a transceiver antenna
11
to exchange messages with a slave unit
2
having a transceiver antenna
22
. The transmission channel is formed by the volume of air between the two antennas
11
and
22
. Each of the master unit and the slave unit can transmit messages to the other unit and receive messages from the other unit. The master unit is distinguished from the slave unit in that the master unit takes the initiative in the communication. For example, the master unit can be the central processing unit of a computer, and the slave unit can be one of its peripherals such as a printer that is remote-controlled by means of any transmission channel.
There are conventional methods of communication that consist of transmitting messages that include 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, and is sequenced at a specified rate with the units including conventional circuitry to lock in to the rate the same clock or two synchronous or dia-synchronous clocks.
FIG. 2
shows an example of a conventional elementary message format. The elementary message begins with a starting bit START whose function is to synchronize the clock of the addressed unit with the received message. Then, the message includes an encoded useful information word INFO (e.g., encoded in eight bits or one byte). This word may be an instruction word whose value indicates the nature of a command to be carried out by the addressed unit. For example a read or write command. Alternatively, it could be an address word whose value indicates the address (or a part of the address) of a memory location of the addressed unit at which a data element is to be read or written. Additionally, the word can be a data word whose value indicates the value of a data element processed by the addressed unit.
The elementary message also includes a check bit CHECK such as a parity check bit. The value of the parity check bit CHECK is fixed at the logic value 1 or 0, and 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 chosen type of parity. The role of the parity check bit CHECK is to enable the addressed unit to detect any transmission errors. In such a case, the addressed unit can request a re-transmission of the message.
The conventional message ends with an end-of-transmission bit STOP that is used solely to indicate the end of the message. Following the end-of-transmission bit STOP, each protocol generally provides for a number of elementary temporal units during which the sending unit no longer sends any bit on the transmission channel. Thus, the transmission channel is left free so that the addressed unit can send a bit ACK to acknowledge the communication. The logic value of the acknowledgment bit indicates whether the message has been accurately received. The circuitry conventionally used to determine whether the message has been accurately received is the check performed by means of the parity check bit CHECK. In
FIG. 2
, four such elementary temporal units follow the bit STOP, with one of these temporal units being occupied by the reception acknowledgment bit ACK.
There presently exists a very large quantity of different communication protocols for electronic systems. Each protocol is suited to the specific constraints of a specific application (such constraints including the size of the words to be transmitted, coherence checks, the need to securitize communications against passive or active intervention by ill-intentioned individuals, constraints related to acknowledgment mode, and maximum duration of transmission in relation to the bit rate). Within one system, the master unit and the slave unit obviously conform the same 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 in order to enable other manufacturers to incorporate these systems into more complex assemblies or develop new industrial and/or commercial applications. Thus, with respect to the size of the communications in which such protocols are used, the integrity of the information transmitted and the efficiency of the transmission has to be the optimum. In other words, it is necessary for the transmission to be affected by a minimum of errors. Furthermore, there are applications in which the integrity of the information exchanged and the efficiency of communication are major constraints in the specifications. Conventionally, quality control of the transmission of the binary signals lies essentially in the analysis and interpretation of the value of the parity check bit CHECK described above.
FIGS. 3A and 3B
show two possible cases to illustrate the determining of the parity bit CHECK. In these examples, the message format of
FIG. 2
is used. In the figures, no special attention has been paid to the values of the starting bit START and end-of-transmission bit STOP. All that has been taken into account is the values of the bits of the useful information word INFO, the parity check bit CHECK, and the acknowledgment bit ACK.
FIG. 3A
shows the case of a useful information word INFO
1
whose transmission has not been erroneous. The logic value 1 is illustratively given to the first seven bits B
1
, B
2
, B
3
, B
4
, B
5
, B
6
, and B
7
of the useful information word INFO
1
, and the last bit B
8
of the useful information word INFO
1
is set at the logic value 0.
If an “even” type of parity is used, the parity check bit CHECK will then take the logic value 1. That is, the sum of the values of the eight bits of the useful information word INFO
1
added to the value of the parity bit CHECK gives the number 8 in conformity with even parity. In the case of
FIG. 3A
, the transmission of the useful information word INFO
1
is not affected by errors so the useful information word INFO
2
that results 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 conformity with the expected result with respect to the value of the received parity check bit and the type of parity adopted. Thus, as shown in
FIG. 3A
, the acknowledgment bit has the value that indicates accurate reception. (In
FIGS. 3A and 3B
, accurate acknowledgment illustratively corresponds to a value 1 of the acknowledgment bit ACK.)
FIG. 3B
shows a case with the same useful information word INFO
1
, but for 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 received useful information word INFO
3
is different from the eighth bit of the transmitted useful information word INFO
1
. Thus, the transmission has been erroneous and the useful information word INFO
3
no longer matches with the parity check bit CHECK. The same result would occur if three, five, or seven of the eight bits constituting the received useful information word INFO
3
had been
Bongini Stephen
Fleit Kain Gibbons Gutman & Bongini P.L.
Jorgenson Lisa K.
Ohung Phung M.
STMicroelectronics S.A.
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