DE102004035984A1 - Half duplex transmission method, involves providing medium on half duplex protocol of profibus for adjustment of optical full duplex path and activating transmitters in half duplex operation only when data telegram is sent - Google Patents

Abstract

The method involves providing a medium on a half duplex protocol of a profibus for adjustment of an optical full duplex path, where the medium is formed of light transmitters (1) and light receivers (2). The transmitters in the half duplex operation are activated only when data telegram is sent and the transmitters and the receivers are connected and disconnected using additional modules at required speed. An independent claim is also included for an arrangement for half duplex transmission.

Description

The The invention relates to a method and an arrangement for realization a half-duplex optical transmission path between Profibus cable segments.

optical Free-space data transmission systems usually work with two independent channels for each transmission direction. To avoid unwanted crosstalk These channels are electric frequenzsetektiert.

In addition will a sturdy one Modulation methods such as frequency shift keying (FSK), which is the frequency selection support applied.

In a known manner, the adaptation of an optical Vollduplexstrecke formed of light emitter 1 and light receiver 2 ( 1 ), to the semi-duplex protocol of the Profibus, the cable segment 3 is applied by so-called. Profibus switches.

A decision maker 4 the Profibus switch recognizes the respective transmission direction in the optical free-space transmission system by observing the data traffic and switches the bus driver 5 in the appropriate direction.

The not shown optical counterpart of the full duplex line is identical to the arrangement according to 1 ,

There with Profibus data telegrams at a time always only in each case a direction is sent during the transmission of the respective optical return channel unused. The optical transmission path So it's always only halfway used. On the respective unused channel becomes a logical resting level Posted.

Of the Invention was based on the object, a method and an arrangement for adapting a full-duplex optical transmission link to the half-duplex protocol of a professional bus to create that Profibus half-duplex principle also transferred to the optical route becomes.

The solution The object is achieved according to the features of claims 1 and 5th

The further claims give expedient refinements the solution according to the invention again.

While in Full-duplex sections the optical transmitters are in continuous operation, The optical transmitter according to the invention in half-duplex mode, if necessary only during each of the data telegram to be sent and both light emitters as well as receiver by means of additional Modules are switched on and off at the required speed.

At the Switching on and off of transmitters, there are always phases in which on the opposite side arise undefined received signals. Because it These are energy transfer processes (settling filters, etc.), these are no longer negligible short, but take several bit times. The duration of this and shutdown operations must go through delay elements covered on sender and receiver side become.

The decisive factor is that in the course of the switching operations no impulse disturbances of the data packet (additional pulses before the beginning and after the end of the switching operations) are caused. The Profibus protocol does not allow falsification of the data stream. There is in the physical transfer layer 1 No error correction mechanisms that could, for example, restore a falsified telegram beginning. For this reason, undefined phases must be masked out by readiness delay so that error-free transmission is made from the first bit. The protocol conventions of the Profibus must be fulfilled.

A important to be solved Task is the prevention of optical reception directly after telegram end, if the transmitter of the opposite side after the last Telegram sign is switched off. This so-called noise reception arises in that the receiver after the receipt signal is not immediately ready to receive but continues to receive some time, but only noise supplies to the evaluation unit. Only when the signal strength detector responds to the absence of the signal, the noise reception is terminated.

One additionally to be solved Problem with such a defined optical transmission path arises from the fact that at missing traffic none of the pages sends, so no sleep level as in the full-duplex mode is sent, so that the detection of the opposite side not possible is. However, the optical contact is used to adjust the optical Axes of the devices to each other in the device when e.g. not yet other subscribers causing data traffic are installed.

The invention is intended to an Ausführungsbei play on the basis of 2 be explained in more detail.

In the idle state, ie during the telegram pauses in which there is no activity on the bus line, the controller expects data telegrams from one of the two possible directions. Bus Driver 5 and light emitters 1 are switched to passive.

Data telegrams coming from the cable segment 3 come and be sent over the light path are by a delay element 6 delayed by a short period of time. the decider 4 , which monitors the traffic, first switches the light transmitter 1 one. The transmission delay of the data serves to allow the receiver of the opposite side to settle, since the data telegrams in the Profibus must be transmitted without errors from the first bit. At the same time, the decision maker is blocked 4 the own light receiver 2 (Muting), so he does not produce apparent received signals by stray light or reflections of their own transmitted light. the decider 4 monitors the telegram to be sent for the purpose immediately after telegram end the light transmitter 1 turn off, the light receiver 2 release again and take the hibernation.

In the opposite direction, so when signals are received over the optical link, the light receiver 2 active. The received signals are only recognized if the received signal strength exceeds a minimum value. This qualification is through the gate 7 symbolizes.

The received data runs in a receive buffer 8th in which they are checked by a test algorithm 9 which checks the character and telegram conformity to the Profibus standard. The result is shared by the test algorithm 9 the decision maker 4 With. Detects the decision maker 4 a valid telegram beginning, he switches the bus driver 5 in transmission direction. As long as the data stream is error-free, it is transmitted via a send buffer 10 on the cable segment 3 Posted. Detects the test algorithm 9 If there is an error, the data stream is aborted, the idle state is set and the system waits for new telegrams.

After the end of the reception telegram, the light receiver 2 blocked by the control by means of the signal receiver I / O for a defined time T _LOCK , within which the signal strength _{detection assumes} its idle state. The blocking time must not exceed the Profibus parameter T _SDRmin . If it is larger, then T _SDRmin must be _adapted by parameterization.

In addition, in the event of a lack of data traffic - ie after expiry of a maximum rest period that occurs according to the standard - the controller sends the transmission of false telegrams by means of a filling data transmitter 11 initiated. These are deliberately constructed in contradiction to the Profibus conventions. The false telegram is determined by the test algorithm 9 definitely recognized as false and prevents forwarding to the connected Profibus segment. However, the resulting false data traffic on the optical path causes an evaluable signal strength level, which is needed to align two data light barriers during installation to each other.

advantage The invention is in particular the waiver of the frequency selection of the channels. As required, always can only send one page both sides for Send and receive use the same frequency range. The allows for a similar devices on both sides of the light path, which simplifies warehousing and replacement. The modulation parameters can on the other hand optimally designed for the signal-to-noise ratio to be achieved, there the oppression of the return channel eliminated. It can This also broadband modulation, which otherwise for this Exclude application, be applied to higher Data rates and reach to achieve.

1

light source

2

light receiver

3

cable segment

4

decision-makers

5

Bus Driver

6

delay

7

AND gate

8th

Receive character buffer

9

checking algorithm

10

send buffer

11

Fülldatensender

Claims (8)

Method for optical half-duplex transmission between Profibus segments, in which means are provided for adapting the optical full-duplex path, formed by light emitter and light receiver, to the half-duplex protocol of the Profibus, characterized in that the light emitters ( 1 ) are switched on in half-duplex mode only during the data telegram to be sent and both light emitters ( 1 ) as well as receiver ( 2 ) by means of additional assemblies ( 4 . 6 - 11 ) are turned on and off at the required speed. A method according to claim 1, characterized in that the settling time of the counter receiver by arranged on the transmitter side Ver delay elements ( 6 ) is covered for the data telegrams to be sent. Method according to one of the preceding claims, characterized in that for the suppression of the reception _noise after the end of a telegram reception, a reception _lock for the duration of a standardized Profibus rest time T _{SDRmin is} inserted. Method according to one of the preceding claims, characterized characterized in that for the purpose of optical alignment of the data light barriers in Case of missing data traffic as a replacement False telegrams between be exchanged for both participants of the optical route, the through the testing algorithms recognized and suppressed on both sides as an error telegram, However, by the optical activity necessary for the adjustment received signal level produce. Arrangement for carrying out the method according to one of Claims 1 to 4, characterized in that a decision maker ( 4 ) is provided, the light transmitter ( 1 ), the transmission delay controls, the own light receiver ( 2 ) is blocked by muting, shuts off the light transmitter after telegram end and switches the light receiver back on. Arrangement according to claim 5, characterized in that a receiving buffer ( 8th ) is provided in which the received data by a test algorithm ( 9 ), which carries out the check for character and telegram conformity to the Profibus standard, and the result to the decision maker ( 4 ) communicates. Arrangement according to claim 6, characterized in that the decision maker ( 4 ) with a valid telegram beginning the bus driver ( 5 ) in transmission direction and that a transmission buffer ( 10 ) is provided, via which an error-free data stream to the cable segment ( 3 ) is sent. Arrangement according to claim 6, characterized in that the test algorithm ( 9 ) aborts a faulty data stream and sets the idle state.