Patent Publication Number: US-2022221894-A1

Title: Technique for correcting a time parameter

Description:
CROSS-REFERENCE TO PRIOR APPLICATIONS 
     This application is a U.S. National Phase application under 35 U.S.C. § 371 of International Application No. PCT/EP2020/063268, filed on May 13, 2020, and claims benefit to Luxembourg Patent Application No. LU 101216, filed on May 15, 2019. The International Application was published in German on Nov. 19, 2020 as WO 2020/229509 under PCT Article 21(2). 
    
    
     FIELD 
     The invention relates to the correction of a time parameter in a connected node. In particular, the invention relates to a device and to a method for correcting a time parameter in a first node in accordance with a second node. 
     BACKGROUND 
     The number of networked devices increases rapidly in many areas. For example, devices that themselves do not have a user interface are increasingly networked. Networked devices that use the internet protocol (IP) for communication at a higher level are also referred to as the Internet of Things (IoT). Regardless of the application, the presence of a user interface, or the connection to a cloud service, networked devices are referred to herein as nodes. 
     The physical layer of communication between the nodes may comprise asynchronous data transmission without clock lines, for example for ease of installation or in order to use existing 2-wire lines. Asynchronous data transmission makes a field bus possible. This enables the networking of sensors and actuators in switchgear boxes, production plants, and vehicles. Field buses for this purpose are Interbus and the bus in a so-called controller area network (CAN bus). Application examples are industrial production under the designation “Industry 4.0” or autonomous driving. Asynchronous data transmission also makes field buses possible for networking consumption meters or heating systems in residential buildings for remote reading and home automation. For the last purpose, the metering bus (also: M-Bus) has been established in the EN 13757 series of standards. 
     The term “asynchronous” refers here to the format of data transmission, for example by means of a start bit. The directly networked nodes must be “synchronous” with each other in the sense of an externally uniform system symbol rate. The latter is referred to herein as synchronization in order to avoid confusion of terms with asynchronous data transmission. 
     In order to maintain synchronization in asynchronous data transmission proceeding from the start bit at least during the transmission of a character, each node must conventionally have a sufficiently precise and stable clock pulse generator. This is described, for example, in document U.S. Pat. No. 3,452,330 A. Such a clock pulse generator, for example a crystal oscillator, does however increase the production costs and power consumption of each node. 
     In order to maintain synchronization of the nodes when clocked by means of lower-power resonant circuits, stuffed bits are sent in a CAN bus. However, these stuffed bits reduce protocol efficiency and increase the complexity of signal processing in each node. 
     SUMMARY 
     In an embodiment, the present invention provides a device for correcting a time parameter in a first node in accordance with a second node, comprising: a clock pulse generator unit configured to provide periodic clock pulses in the first node; a peripheral unit configured to decode symbols of an asynchronously transmitted telegram from the second node and to measure a number of clock pulses during the transmission of a symbol sequence of consecutive symbols of the telegram; and a correction unit configured to correct the time parameter as a function of a ratio of the measured number of clock pulses and the number of consecutive symbols in the symbol sequence. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will be described in even greater detail below based on the exemplary figures. The invention is not limited to the exemplary embodiments. Other features and advantages of various embodiments of the present invention will become apparent by reading the following detailed description with reference to the attached drawings which illustrate the following: 
         FIG. 1  shows a schematic representation of an exemplary embodiment of a device for correcting a time parameter in a first node in accordance with a second node; 
         FIG. 2  shows a flow chart of an exemplary embodiment of a method for correcting a time parameter in a first node in accordance with a second node, which can be executed by means of the device in  FIG. 1 ; 
         FIG. 3  shows a schematic representation of an exemplary arrangement of several nodes which are connected in series and which can at least partially embody the device in  FIG. 1 ; and 
         FIG. 4  shows a schematic representation of an exemplary telegram which can be transmitted from or to one of the nodes. 
     
    
    
     DETAILED DESCRIPTION 
     In an embodiment, the present invention provides a more efficient technique for synchronizing nodes that transmit data asynchronously. 
     According to one aspect of the invention, a device for correcting a time parameter in a first node in accordance with a second node is provided. The device comprises a clock pulse generator unit designed to provide periodic clock pulses in the first node. The device furthermore comprises a peripheral unit which is designed to decode symbols of an asynchronously transmitted telegram from the second node and to measure a number of clock pulses during the transmission of a symbol sequence of consecutive symbols of the telegram. The device furthermore comprises a correction unit designed to correct the time parameter as a function of the ratio of the measured number of clock pulses and the number of consecutive symbols in the symbol sequence. 
     The time parameter may be a clock-pulse rate of the clock pulse generator unit, a symbol rate of decoding, a control parameter for controlling the clock pulse rate, and/or a control parameter for controlling the symbol rate. 
     Exemplary embodiments of the device can prevent an error and/or a discontinuance of decoding in the event of a (for example temperature-dependent) drift of the clock pulse of the clock pulse generator unit. For example, a first deviation of the clock pulse rate of the clock pulse generator unit and/or the symbol rate of the decoding, which is not yet preventing the decoding, can be determined by measuring the ratio and can be corrected or compensated by the correction unit as a function of the measured ratio. In particular, correction of the time parameter may directly correct or (for example, completely or at least partially) compensate for the deviation of the clock pulse rate and/or the symbol rate. 
     The same or further exemplary embodiments of the device can, based on the time parameter corrected in response to the first deviation, enable further decoding and/or further correction according to the invention in the event of a second deviation that is greater than the first deviation. An error or discontinuance of decoding can be prevented. For example, the second deviation can be so great that, without correction of the time parameter in response to the first deviation, decoding following the second deviation would fail, whereas decoding will succeed according to the invention, for example because a deviation interfering with the decoding is limited to the difference between the second deviation and the first deviation. 
     Acquisition (for example, sampling) of the telegram transmitted from the second node and/or decoding the symbols of the telegram (for example, based on sample values of the sampling) can be clocked by the clock pulse generator unit and/or configured by the time parameter. As soon as the time parameter has been corrected by the correction unit, acquisition and/or decoding can take place according to the corrected time parameter. For example, a first telegram or a first character within the telegram may be the basis for correction of the time parameter by the correction unit. This means that the consecutive symbols in the symbol sequence may be symbols of the first telegram or of the first character. The corrected time parameter can be used when acquiring and/or when decoding a second telegram (which is transmitted from the second node immediately after the first telegram) or a second character of the first telegram. 
     The same or further exemplary embodiments of the device may implicitly correct the time parameter only based on the asynchronous transmission from the second node to the first node and/or in the absence of a control line between the first node and the second node. 
     The time parameter can (for example, directly or indirectly) control or influence the decoding. The time parameter may be a temporal parameter of decoding (decoding parameter). 
     The time parameter may comprise a clock pulse rate of the first node, a symbol rate of the first node, and/or a ratio of clock pulse rate and symbol rate (also: divider) of the first node. The time parameter may comprise a divider (for example, an integer divider). The symbol rate may be determined from the clock pulse rate (i.e., starting from the clock pulse of the clock pulse generator unit) according to the divider. For example, there is only one clock pulse generator unit in the first node both for measuring the number of clock pulses and for decoding. According to the divider, the symbol rate may be an integral fraction of the clock pulse rate. For example, the device may comprise a frequency divider that generates the symbol rate from the clock pulse rate according to the divider. 
     For example, a signal of the telegram received by the second node may be sampled or undersampled by the first node according to the clock pulse of the clock pulse generator unit. Alternatively or additionally, the received signal can be divided into the symbols of the telegram according to the symbol rate. Alternatively or additionally, sample values of the received signal can be divided according to the divider into the symbols of the telegram. 
     The symbol sequence may be shorter than one character within the telegram. The conventional use of stuffed bits for maintaining synchronization during the transmission of a character can thus be avoided. In particular, protocol efficiency can be improved since stuffed bits do not correspond to any symbol for the transmission of data (neither control data nor payload data). 
     Sampling of the telegram transmitted from the second node or decoding the symbols of the telegram is clocked by the clock pulse generator unit and/or controlled by the time parameter. 
     The first node may be a node (in particular, a slave node) in a communication chain. The first node may be arranged within or at the end of the communication chain. The communication chain may comprise several nodes that are connected in a series for asynchronous data transmission. The communication chain can be a so-called daisy chain. The second node may be a master node and/or a node upstream of the first node in the communication chain. The third node may be a further node (in particular a further slave node) and/or a node downstream of the first node in the communication chain. 
     The peripheral unit may comprise a first (for example, serial) interface for asynchronous transmission of the telegram from the second node and/or a second (for example, serial) interface for asynchronous transmission of a telegram to a third node. Both the first interface and the second interface may be clocked by the clock pulse generator unit and/or controlled by the corrected time parameter. 
     The peripheral unit may comprise an encoder and/or a decoder for each interface. The respective encoder and/or decoder may be designed to encode or decode the symbols of a character of a transmitted or received telegram as a function of the time parameter. 
     The time parameter may comprise a clock pulse rate of the clock pulse generator unit. The correction unit may be designed to correct the clock pulse rate of the clock pulse generator unit as a function of the ratio of the measured number of clock pulses and the number of consecutive symbols in the symbol sequence. With respect to an actual clock pulse rate of the clock pulse generator unit, the corrected clock pulse rate may be corrected by the quotient of a predetermined number of clock pulses per symbol and the measured ratio. The predetermined number of clock pulses per symbol may correspond to the quotient of the corrected clock pulse rate (or the target clock pulse rate) of the clock pulse generator unit and the system symbol rate. 
     Alternatively or additionally, the time parameter may comprise a symbol rate (also: baud rate) of the peripheral unit. The correction unit can be designed to correct the symbol rate of the peripheral unit as a function of the ratio of the measured number of clock pulses and the number of consecutive symbols in the symbol sequence. The corrected symbol rate may be corrected with respect to a predetermined system symbol rate by the quotient of the measured ratio and a predetermined number of clock pulses per symbol. 
     The signal of a character of the telegram from the second node can be divided according to the symbol rate into the symbols of the telegram. A small error in the symbol rate, for example a deviation of the symbol rate by less than half a symbol per character, can be corrected on the basis of a start symbol and a stop symbol (or several stop symbols) of the character. For example, the signal of the particular character between the start symbol and the stop symbol may be divided into symbols of equal length. 
     Alternatively or additionally, the time parameter may comprise a divider for a symbol rate of the peripheral unit relative to a clock pulse rate of the clock pulse generator unit. The correction unit may be designed to correct the divider as a function of the ratio of the measured number of clock pulses and the number of consecutive symbols in the symbol sequence. The corrected divider may be equal to or proportional to the measured ratio. 
     The symbol sequence of consecutive symbols of the telegram may extend from a first falling (or first rising) edge to a later, first rising (or first falling) edge of the transmission of the telegram. 
     The device can be implemented by means of a microcontroller. A processor unit, for example of the microcontroller, can implement the correction unit. 
     The microcontroller may comprise the clock pulse generator unit, the peripheral unit, and/or the correction unit. The microcontroller may furthermore comprise a capture/compare unit (CC unit) to which a received signal of the telegram from the second node is applied. The CC unit can be designed to measure the number of clock pulses during the transmission of the symbol sequence. 
     For example, the symbol sequence of the telegram may only comprise symbols for the transmission of payload data. The symbol sequence of the telegram on which measurement of the number of clock pulses is based can immediately follow a start bit and only contain symbols for payload data. 
     The symbol sequence of the telegram may be shorter than a character of the telegram. Alternatively or additionally, the symbol sequence of the telegram may be a part of the first character of the telegram. 
     The peripheral unit may also be designed to measure a number of clock pulses during the transmission of a predetermined synchronization character of the telegram. The correction unit may also be designed to correct the time parameter as a function of the ratio of the measured number of clock pulses and a predetermined number of symbols in the synchronization character and/or as a function of a quotient of the measured number of clock pulses and a predetermined target value of the number of clock pulses during the transmission of the synchronization character. The synchronization character can be transmitted at the beginning of the telegram. 
     Correction on the basis of the synchronization character can always be carried out at the beginning of transmission of the telegram and/or if decoding of the symbols in the telegram is not possible due to error in or deviation of the time parameter. For example, at the beginning of transmission of the telegram, the time parameter can be corrected by means of the synchronization character. During the transmission of the telegram, the time parameter can be corrected as a function of the ratio of the measured number of clock pulses and the number of consecutive decoded symbols in the symbol sequence. 
     According to a further aspect, an arrangement of nodes connected in series (e.g., topologically linearly) for asynchronous data transmission is provided. The arrangement comprises a first node which is connected to a second node for asynchronous data transmission and which comprises an exemplary embodiment of the device for correcting a time parameter in the first node in accordance with the second node according to the device aspect. Optionally, the arrangement comprises the second node as master node of the arrangement. The arrangement furthermore comprises a third node which is connected to the first node for asynchronous data transmission and which comprises a further exemplary embodiment of the device for correcting a time parameter in the third node in accordance with the first node according to the device aspect. 
     In accordance with yet another aspect of the invention, a method for correcting a time parameter in a first node in accordance with a second node is provided. The method comprises or initiates a step of providing periodic clock pulses (for example, a step in the clocking) in the first node. The method furthermore comprises or initiates a step of decoding symbols of an asynchronously transmitted telegram from the second node and of measuring a number of clock pulses during the transmission of a symbol sequence of consecutive symbols of the telegram. The method furthermore comprises or initiates a step of correcting the time parameter as a function of the ratio of the measured number of clock pulses and the number of consecutive symbols in the symbol sequence. 
     The method may furthermore comprise any step and any feature disclosed in the context of the device aspect, and vice versa. 
       FIG. 1  shows a schematic block diagram of an exemplary embodiment of a device, designated overall by reference sign  100 , for correcting a time parameter in a first node in accordance with a second node. 
     The device  100  comprises a clock pulse generator unit  110  which provides periodic clock pulses in the first node. The device  100  furthermore comprises a peripheral unit  120  which decodes symbols of a telegram transmitted asynchronously from the second node and which measures by means of a counter  124  a number of clock pulses during the transmission of a symbol sequence of consecutive symbols of the telegram. The device  100  furthermore comprises a correction unit  130  which corrects the time parameter as a function of the ratio of the measured number of clock pulses and the number of consecutive symbols in the symbol sequence  406 . 
     The time parameter may comprise a clock pulse rate  115  of the provided clock pulses or a control parameter of the clock pulse generator unit for controlling the clock pulse rate. Alternatively or additionally, the time parameter may comprise a symbol rate  125  of the peripheral unit  120  or a control parameter of the peripheral unit for controlling the symbol rate  125 . At least the latter example of the time parameter may, as shown schematically in  FIG. 1 , be written to a register of the peripheral unit  120 . 
     The control parameter for controlling the symbol rate may be a divider of the clock pulse rate. For example, the symbol rate may be the clock pulse rate  115  divided by the divider. 
     The symbol rate  125  may be a function of the time parameter. For example, the symbol rate may be the quotient of the clock pulse rate  115  and the divider, wherein the clock pulse rate  115  and the divider are in each case examples of the time parameter. 
     The symbol sequence may be determined by the consecutive symbols. For example, the symbol sequence may extend from a first falling (or rising) edge to a first rising (or falling) edge in a signal of the telegram received by the peripheral unit  120 . 
     The number of clock pulses during the symbol sequence may be written to the counter  124 . The counter  124  may, for example, be set to zero at the beginning of the telegram and/or at the beginning of the symbol sequence. With each clock pulse of the clock pulse generator unit  110 , the counter  124  can be incremented by one. The correction unit  130  may read out from the counter  124  the measured number of clock pulses at the end of the symbol sequence, for example as denominator of the ratio of the number of clock pulses to the number of symbols in the symbol sequence. 
     The peripheral unit  120  furthermore comprises a decoder  122  which carries out the decoding of the telegram received from the second node. The decoder  122  may output to the correction unit  130  the number of consecutive symbols belonging to the symbol sequence. Alternatively or additionally, on the basis of the symbols output by the decoder  122 , the correction unit can determine a beginning and/or an end of the symbol sequence and/or the number of symbols in the symbol sequence. 
     Optionally, the device  100  or the first node is designed for bidirectional communication with the second node. For this purpose, the device  100  or the first node may comprise a first interface  121  comprising the decoder  122  and also an encoder  123 . The encoder  123  is designed to generate the symbols for a telegram that is sent to the second node via the first interface  121 . 
     Furthermore, the device  100  or the first node may be in asynchronous data exchange with a third node via a second interface  126 . For this purpose, the device  100  or the first node can comprise the second interface  126 . The second interface  126  can comprise a decoder  127  and an encoder  128  for receiving or sending telegrams from or to the third node. 
     The second node may be a master node or a slave node (for example, a higher-ranking slave node compared to the first node) which specifies a system symbol rate to the first node solely on the basis of the asynchronous data transmission. The first node may be a slave node in relation to the second node. The third node may be a slave node (for example, a lower-ranking slave node compared to the first node). 
     The same symbol rate  125  can be applied to both interfaces  121  and  126 . For example, the correction unit  130  can correct the time parameter as a function of the ratio measured at the first interface  121 . As a result, compliance with the symbol rate  125  can thereby also be achieved at the second interface  126 , for example. In particular, the symbol rate (for example, on the output side, i.e., in the course of transmitting an asynchronously transmitted telegram) specified at the first interface (for example, on the input side, i.e., in the course of receiving an asynchronously transmitted telegram) can be passed on at the second interface. The master node can thus specify a uniform system symbol rate via several slave nodes connected in series for asynchronous data transmission. 
     Each of the two interfaces  121  and  126  of the first node may be a so-called universal asynchronous receiver transmitter (UART) interface. 
       FIG. 2  shows a flow chart of an exemplary embodiment of a method, designated overall by reference sign  200 , for correcting a time parameter in a first node in accordance with a second node. 
     In a step  210 , periodic clock pulses are provided in the first node. Symbols of an asynchronously transmitted telegram from the second node are decoded in a step  220 . Furthermore, in step  220 , a number of clock pulses is measured during the transmission of a symbol sequence of consecutive symbols of the telegram. In a step  230 , the time parameter is corrected as a function of the ratio of the measured number of clock pulses and the number of consecutive symbols in the symbol sequence (in short: the measured ratio). 
     In each aspect of the invention, the number of consecutive symbols in the symbol sequence may be determined on the basis of the decoding. For example, the number of consecutive symbols in the symbol sequence may be determined as the number of decoded symbols which can be temporally assigned to the symbol sequence. 
     The telegram may comprise a plurality of characters. The characters may also be referred to as bytes. The symbol rate may also be referred to as the baud rate. The data to be transmitted may correspond to a character string of consecutive characters. The data to be transmitted may comprise payload data and/or control data. Each character may comprise a certain number of bits, for example 4, 7, 8, 10, or 12 bits. Each character can be encoded according to an encoding method (i.e., output as a transmitted signal on a transmission line) or decoded (i.e., acquired from a received signal on a reception line). Each symbol may correspond to one or more bits, for example depending on the encoding method. 
     For the sake of simplicity, it is assumed below without restricting generality that each bit corresponds to a symbol. 
     In conventional asynchronous data transmission, the temperature drift of the clock pulse generator unit  110 , i.e., of the clock-pulse-generating components can lead to baud rate errors, which above a certain deviation lead to communication interruptions. In order to prevent this, expensive quartz crystals must conventionally be used for clock pulse generation. Exemplary embodiments of the invention may make it possible to dispense with a quartz crystal in the subordinate nodes (i.e., the slave nodes). 
     The measurement  220  of the ratio of clock pulses per decoded symbol and/or the correction  230  as a function of the measured ratio can be carried out by the device  100  in the first node (for example, in one of the slave nodes) for all X received telegrams, where X is a predetermined integer. 
     The correction unit may measure the symbol sequence as part of the first byte of the received telegram. From the number of bits and the measured clock pulses, the measured ratio, i.e., the number of clock pulses per bit (in short: clock pulses/bit) is ascertained. The measured ratio may also be referred to as the actual clock pulses per bit (in short: actual clock pulses/bit). 
     In one exemplary embodiment, a number of target clock pulses per bit (in short: target clock pulses/bit) is predetermined. The correction unit  130  calculates the difference between the target clock pulses and the actual clock pulses per bit, i.e. 
       deviation=target clock pulses/bit−actual clock pulses/bit.
 
     This is the deviation in clock pulses per bit. 
     In order to correct the baud rate  125  in the first node (i.e., in the slave node), the correction unit  130  assumes the previous baud rate. This may numerically correspond to the system baud rate but, due to a deviation in the clock pulse rate  115 , may correspondingly deviate from the system baud rate. The value of the system baud rate is thus the numerical value in the “slave baud rate” register before correction. After correction of this register value as an example of the time parameter, the “slave baud rate” register contains the value 
       corrected baud rate=system baud rate[1±correction factor(deviation)]=system baud rate±correction rate(deviation)
 
     The correction factor or the correction rate is a function of the deviation. For example, 
       correction factor(deviation)=deviation/[target clock pulses/bit]. 
     By correcting the baud rates for both interfaces  121  and  126  of the slave node (as an example of the first node), the slave node next in the linear topology (for example, the first node as the next low-level node after the second node) can adapt its baud rate to the baud rate of the previous master or slave node (for example, the second node). 
     By correcting the baud rate  125  as an example of the time parameter, an internal adaptation is realized, by means of which the baud rate of the respective slave node that can be observed from the outside (for example, at the second interface  126 ) with an increase in its temperature remains at the defined system baud rate (preferably specified solely by the asynchronous data transmission from the master node). 
       FIG. 3  schematically shows an arrangement  300  (also: system) of several nodes connected in series (i.e., topologically linearly) for asynchronous data transmission. A first node of the arrangement may as master node  310  specify the system baud rate for the entire arrangement  300  in that each slave node  320  downstream of the master node  310  comprises an exemplary embodiment of the device  100 . 
     For example, the master node  310  (preferably as the only node in the arrangement  300 ) comprises an oscillating quartz crystal  312 . By means of the oscillating quartz crystal  312 , the master node generates a symbol sequence when transmitting the telegram, the symbol rate of which specifies the system symbol rate. 
     In particular, the first interface  121  is connected in each case to the adjacent node (i.e., the so-called second node), which is topologically closer to the master node  310  than the respective node (i.e., the so-called first node). The second interface  126  is in each case connected to the adjacent node (i.e., the so-called third node), which is topologically further away from the master node  310  than the respective node (i.e., the first node). 
     Such an arrangement  300  may also be referred to as a daisy chain. A telegram (for example, one starting from the master node  310 ) that passes through the arrangement  300  from slave node  320  to slave node  320  may also be referred to as a daisy-chain telegram. 
     While more cost-effective internal oscillators are highly temperature-dependent, exemplary embodiments of the device can prevent a drift of the baud rate in the event of slave nodes  320  heating up and thus save more expensive oscillating quartz crystals in the slave nodes. 
     A preferred exemplary embodiment implements the device  100  by means of a microcontroller (the one labeled “μC” in short in  FIG. 3 ). A so-called capture/compare unit (CC unit) in the microcontroller can implement the counter  124  in order to measure the clock pulses/bit ratio, to ascertain the target baud rate of the system from the daisy-chain telegram, and thus to compensate for a temperature drift of the internal oscillator. For this purpose, the signal of the telegram from the second node is applied to a signal input  322  of the CC unit, for example by a receiving line (which is labeled “Rx” in  FIG. 3 ) of the first interface  121  being connected to the signal input  322 . 
       FIG. 4  schematically shows the beginning of a signal of a telegram  400 . In the schematic representation of  FIG. 4 , time increases from left to right. A voltage level of the signal is shown schematically in the vertical direction. 
     The telegram comprises several characters (i.e., bytes)  402  and  404 . The symbol sequence  406  measured by the peripheral unit  120  (for example, the CC unit) is part of the first character  402 . In other words, the measured symbol sequence  406  ends with or before the last symbol (preferably the last data symbol) of the first character  402 . 
     For example, the beginning of the measured symbol sequence  406  is defined by the first falling edge  408  in the first character  402  of the telegram  400 , and the end of the measured symbol sequence  406  is defined by the first rising edge  410  after the first falling edge  408 . The first falling edge  408  may correspond to a start bit. Alternatively or additionally, the first rising edge  410  after the falling edge  408  may be before a stop bit  412  (or before several stop bits) of the first character  412 . Each character  402  and  404  can be framed by start and stop bits. 
     An implementation of the method  200  may measure the number of clock pulses in the symbol sequence  406  according to step  220  every X received telegrams  400  (i.e., after X received telegrams  400  in each case), for example by activating the CC unit in the slave node  320 . The CC unit in the slave node  320  measures the clock pulses from falling edge  408  to the rising edge  410  of the first received byte  402 . 
     According to step  220 , the peripheral unit  120  of the slave node  320  decodes the symbols (i.e., the bits) of the first byte  402 . In other words, the slave node  320  evaluates the first byte  402  to arrive on its receiving line and ascertains how many symbols (i.e., bits) were encompassed by the symbol sequence  406  (i.e., by the CC measurement in step  220 ). From the number of bits and the measured number of clock pulses (also: CC clock pulses), the ratio of CC clock pulses per bit (also: CC clock pulses/bit) can be calculated. This ratio is the measured ratio or actual ratio (in short: actual clock pulses/bit). 
     In a first variant of the exemplary embodiment, the symbol rate  125  of the slave node  320  is controlled by the divider with respect to the clock pulse rate  115 . The divider is an example of the time parameter. In the first variant, the measured ratio can be set as the corrected divider, for example by writing the measured ratio to the corresponding register for controlling the symbol rate  125 . 
     In a second variant of the exemplary embodiment, in the correction unit  130  of the slave node  320 , the number of target clock pulses per bit (in short: target clock pulses/bit), i.e., the target value of the ratio, is predetermined as a constant. The target value of the ratio can be calculated from the quotient of a target clock pulse rate (for example CC_Clock) and the system baud rate. A numerical example of this is: 
         CC _clock/baud rate=48,000,000 clock pulses/312.5 kBd=153.6 clock pulses/bit. 
     The deviation of the ratio measured in step  220  from the predetermined target value of the ratio is calculated as clock_pulse_per_bit_difference: 
       clock_pulse_per_bit_difference=target clock pulses/bit−actual clock pulses/bit, that is, the deviation in clock pulses per bit.
 
     In step  230 , the correction unit  130  corrects the numerical baud rate  125  in the slave node  320  as an example of the time parameter. Prior to the correction, the numerical baud rate  125 , for example the value “slave_baud” in the corresponding register of the interfaces  121  and  126 , is equal to the system baud rate. The corrected numerical baud rate is 
       slave_baud=system baud rate±correction factor(clock_pulse_per_bit_difference)
 
     By correcting the baud rates, for both slave UARTs  121  and  126 , the next slave node (i.e., the third node) can adapt its baud rate to the baud rate of the previous slave node (i.e., the first node). 
     As a result of the internal adaptation, as the temperature increases, the baud rate of the slave node remains at the defined system baud rate, which can be observed from the outside. 
     As shown on the basis of the above exemplary embodiments and their variants, the device  100  can be implemented in any system (in particular in any arrangement  300 ) which has a defined system symbol rate (i.e., a target baud rate). A numerical example of the system symbol rate is 312.5 kBd=312,500 Bd, where Bd stands for the unit baud, i.e., symbols per second (for example, bits per second). 
     In step  220 , measurement of the number of clock pulses within the symbol sequence  406  in each slave node can preferably be carried out by means of a capture/compare unit which, for example, measures the number of clock pulses between edge changes in the signal of the received telegram. 
     As an alternative or in addition to each exemplary embodiment and each variant, at least one of the following options can be implemented. A first implementation option dispenses with the oscillating quartz crystal  312  in the master node  310 . For example, the technique can be implemented with a master node, which in turn can be integrated as a slave into a higher-level system. For this purpose, the master node  310  is optionally equipped with an exemplary embodiment of the device  100  that adapts the symbol rate of the master node to the higher-level system, for example without the higher-level system supporting a master/slave mechanism. 
     The described implementation of the method  200  evaluates the content of the received byte  402  (i.e., the byte  402  is decoded) for measuring the number of clock pulses in the symbol sequence  406  by means of the counter  124  (for example, by means of the capture/compare unit). This assumes that this byte  402  can still be decoded (i.e., received), i.e., the deviation (or the existing error) of the symbol rate that has arisen up to that point is still below a threshold of a decoding error (i.e., a threshold of non-receivability). Alternatively or additionally, a second implementation option avoids this limitation (for example, a limitation on the volatility of the clock pulse rate  115 ) by transmitting a synchronization character  402  (for example, a synchronization byte prescribed in the communication protocol) at the beginning of the telegram  400  so that the measured ratio does not have to be ascertained from the decoded symbols of the received payload data, and is thus independent of the successful reception (i.e., successful decoding) of a symbol sequence  406 . A volatility of the clock pulse rate  115  (for example, an abrupt deviation of the clock pulse rate  115 ) or a drift range of the clock pulse rate  115 , which permits or which continues to permit maintenance of the synchronization for asynchronous data transmission, can thus be further increased. An increase in the telegram length by the synchronization character can be accepted for this. 
     The number of clock pulses during the transmission of the predetermined synchronization character of the telegram  400  can be measured by means of the CC unit  124 . The ratio of the measured number  124  of clock pulses and a predetermined number of symbols in the synchronization character results in the measured ratio, which is the basis for correcting the time parameter, for example without symbols of the synchronization character being decoded or decodable. In one variant of the second implementation option, a quotient of the measured number  124  of clock pulses and a predetermined target value of the number of clock pulses during the transmission of the synchronization character is determined. The numerical symbol rate  125  or the corresponding divider can be corrected by this quotient. Alternatively, the clock pulse rate  115  may be corrected by the reciprocal of this quotient. 
     As an alternative or in addition to correcting the numerical baud rate  125  or the corresponding divider (as examples of the time parameter), a third implementation option can correct (i.e., calibrate) internal clock pulse generation by means of the clock pulse generator unit  110 . In other words, the clock pulse rate  115  (as another example of the time parameter) can be corrected. 
     The measurement  220  of the number of clock pulses in the symbol sequence  406  can be triggered and ended by the falling and rising edges. For example, the edge change can trigger a hardware interrupt which starts or ends a corresponding measurement routine. For example, a clock (for example, a CC timer) of the peripheral unit  120  (for example, the CC unit) is started or stopped by application of the signal  322 , wherein the clock is a counter  124  which is incremented with each clock pulse of the clock pulse generator unit  110 . A fourth implementation option implements the measurement  220  of the number of clock pulses in the symbol sequence  406  by interrogating or sampling the received signal at the first interface  121 , e.g., by a cyclic interrogation, i.e., by so-called polling. Upon detection of a corresponding edge change in the cyclic interrogation, the counter  124  can be started or stopped. 
     Although the invention has been described with reference to exemplary embodiments, it will be apparent to a person skilled in the art that various changes can be made and equivalents can be used as substitutes. Furthermore, many modifications can be made in order to adapt a specific situation, a specific topology of asynchronous data transmission, and/or a specific communication protocol to the teaching of the invention. Consequently, the invention is not limited to the disclosed exemplary embodiments but rather encompasses all exemplary embodiments that fall within the scope of the appended claims. 
     While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive. It will be understood that changes and modifications may be made by those of ordinary skill within the scope of the following claims. In particular, the present invention covers further embodiments with any combination of features from different embodiments described above and below. Additionally, statements made herein characterizing the invention refer to an embodiment of the invention and not necessarily all embodiments. 
     The terms used in the claims should be construed to have the broadest reasonable interpretation consistent with the foregoing description. For example, the use of the article “a” or “the” in introducing an element should not be interpreted as being exclusive of a plurality of elements. Likewise, the recitation of “or” should be interpreted as being inclusive, such that the recitation of “A or B” is not exclusive of “A and B,” unless it is clear from the context or the foregoing description that only one of A and B is intended. Further, the recitation of “at least one of A, B and C” should be interpreted as one or more of a group of elements consisting of A, B and C, and should not be interpreted as requiring at least one of each of the listed elements A, B and C, regardless of whether A, B and C are related as categories or otherwise. Moreover, the recitation of “A, B and/or C” or “at least one of A, B or C” should be interpreted as including any singular entity from the listed elements, e.g., A, any subset from the listed elements, e.g., A and B, or the entire list of elements A, B and C. 
     LIST OF REFERENCE SIGNS 
     
         
           100  Device for correcting a time parameter 
           110  Clock pulse generator unit 
           115  Time parameter of the clock pulse generator unit,
       in particular, clock pulse rate or control parameter of the clock pulse rate   
     
           120  Peripheral unit 
           121  First serial interface 
           122  Decoder of the first interface 
           123  Encoder of the first interface 
           124  Counter, in particular capture/compare unit 
           125  Time parameter of the peripheral unit,
       in particular, register for symbol rate or control parameter of the symbol rate   
     
           126  Second serial interface 
           127  Decoder of the second interface 
           128  Encoder of the second interface 
           130  Correction unit 
           200  Method for correcting a time parameter 
           210  Step of clocking 
           220  Step of decoding and measuring 
           230  Step of correcting 
           300  Arrangement in series of connected nodes 
           310  Master node 
           312  Oscillator, in particular quartz oscillator, with an oscillating quartz crystal 
           320  Slave node 
           322  Signal application to a capture/compare unit 
           400  Telegram 
           402  First character of the telegram 
           404  Second character of the telegram 
           406  Symbol sequence 
           408  First falling edge of the telegram,
       for example, start bit of the first character of the telegram   
     
           410  First rising edge of the telegram 
           412  Stop bit of the first character of the telegram