JP2011091742A - Communication device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a communication device in which calculation accuracy of a baud rate can be improved. <P>SOLUTION: The communication device includes a communication part for transmitting and receiving a serial signal containing a start bit and an end bit in one frame, a detecting part for detecting the start bit and the end bit contained in the serial signal transmitted from a communication opponent device, a time measuring part for starting time measuring operation when the start bit is detected by the detecting part and ending the time measuring operation when the end bit is detected by the detecting part, and a setting part for calculating a baud rate based on the result of time measurement of the time measuring part and setting the calculated baud rate in the communication part. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

 The present invention relates to a communication device.

  As is well known, when serial communication is performed between devices having a UART (Universal Asynchronous Receiver Transmitter) interface, it is necessary to set a baud rate that is the same as the baud rate of the transmitting device on the receiving device. When the baud rate of the transmission side device is known, the baud rate of the reception side device may be set by manual operation. When the baud rate is unknown, it is necessary to automatically set the baud rate at the reception side device.

  Conventionally, as a method for automatically setting a baud rate, a method for searching for an appropriate baud rate by changing the baud rate many times until a receivable timing is found at a receiving device (see Patent Documents 1 to 3 below), or reception There is a method of calculating a baud rate by measuring a serial signal received by a side device (see Patent Document 4 below).

  Note that the baud rate can be calculated by measuring the start bit period included in the serial signal.However, if the difference between the start bit fall delay time and the rise delay time increases due to transfer path conditions, the start bit There is a possibility that the measurement accuracy of the bit period is lowered, and consequently the calculation accuracy of the baud rate is lowered.

  On the other hand, in the technique of Patent Document 4, the first and second counters for measuring the period from the falling edge of the start bit to the rising edge at the end of one frame of the command for measuring the transfer rate A third counter and a fourth counter for measuring the time and the rise time, from the fall of the start bit to the last fall of the transfer data, or from the rise of the start bit to the last rise of the transfer data By calculating the transfer rate (baud rate) over a period, the calculation accuracy of the baud rate is improved.

Japanese Patent Laid-Open No. 10-308793 JP 2004-646919 A JP 2005-333513 A Japanese Patent Laid-Open No. 11-112599

  In the techniques of Patent Documents 1 to 3, since it is necessary to change the baud rate many times until a receivable timing is found, there is a problem that it takes a long time to set the baud rate. Further, there is a problem that only a predetermined baud rate can be handled, and any baud rate setting cannot be handled. The technique of Patent Document 4 does not cause the problems of Patent Documents 1 to 3 described above, but has a problem that the circuit configuration for calculating the baud rate is complicated. In order to avoid such complication of the circuit configuration, if a method of calculating the baud rate by measuring only the start bit period is employed, the problem that the baud rate calculation accuracy is lowered cannot be solved.

  The present invention has been made in view of the above-described circumstances, and an object of the present invention is to provide a communication device capable of improving the accuracy of baud rate calculation.

  In order to achieve the above object, a communication device according to the present invention includes a communication unit that transmits and receives a serial signal including a start bit and an end bit in one frame, and the serial signal transmitted from a communication partner device. A detection unit for detecting a start bit and the end bit; and a timing operation when the detection unit detects the start bit, while the timing unit detects the end bit. And a setting unit configured to calculate a baud rate based on a timing result of the timing unit and to set the calculated baud rate in the communication unit.

  In the communication apparatus, in the one frame, the section of the start bit is at a low level, the section of the end bit is at a high level, and the section between the start bit and the end bit is at a low level. When the set serial signal is transmitted from the communication counterpart device, the detection unit detects the falling edge of the serial signal as the start bit, and detects the rising edge of the serial signal as the end bit. It is characterized by that.

Further, in the communication device, the setting unit calculates an average value of the baud rate based on a time measurement result of the time measuring unit obtained for each of a plurality of frames, and calculates the average value of the calculated baud rate as the communication unit. It is characterized by setting to.
In the communication apparatus, the communication unit is a UART (Universal Asynchronous Receiver Transmitter) interface.

  In the present invention, the baud rate is calculated in order to calculate the baud rate from the time measurement result (time measurement result of the time measurement unit) in a section extending over a plurality of bits from the start bit to the end bit included in the serial signal transmitted from the communication partner device. Accuracy can be improved.

It is a block block diagram of the communication apparatus 1 which concerns on one Embodiment of this invention. The format (a) of the UART signal transmitted / received between the communication device 1 and the communication partner device 2 during normal communication and the format (b) of the UART signal transmitted from the communication partner device 2 when the communication connection is established. 4 is a flowchart showing a baud rate setting operation of the communication device 1. 3 is a timing chart showing a baud rate setting operation of the communication apparatus 1;

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a block configuration diagram of a communication device 1 according to the present embodiment. The communication device 1 according to the present embodiment performs serial communication (for example, a modem) with a communication partner device 2 (for example, a personal computer), and includes a UART interface 11, an external interrupt circuit 12, a timer 13, and a CPU (Central Processing). Unit) 14. In FIG. 1, only the UART interface 21 is illustrated as an internal block of the communication partner device 2 for convenience of explanation.

  In the communication apparatus 1, the UART interface 11 (communication unit) communicates with the UART interface 21 of the communication partner apparatus 2 in a UART signal (serial bit) including a start bit (start bit) and a stop bit (end bit) in one frame. Signal). Specifically, the UART interface 11 generates transmission UART signals by serially converting transmission data (parallel data) input from the CPU 14, while receiving data by converting received UART signals in parallel. (Parallel data) is generated and output to the CPU 14. The UART interface 11 is provided with a setting register 11a for setting setting information such as a baud rate necessary for serial communication.

  The external interrupt circuit 12 (detection unit) branches and receives a UART signal transmitted from the UART interface 21 of the communication counterpart device 2 to the UART interface 11, and receives a start bit and a stop bit included in the UART signal. It is to detect. Specifically, the external interrupt circuit 12 detects the falling edge of the UART signal as a start bit, and detects the rising edge of the UART signal as a stop bit. The external interrupt circuit 12 outputs a high-level pulse signal to the timer 13 at the timing when the falling edge of the UART signal is detected and at the timing when the rising edge is detected.

  The timer 13 (timer unit) starts a timekeeping operation when a start bit is detected by the external interrupt circuit 12, and ends a timekeeping operation when a stop bit is detected by the external interrupt circuit 12. Is. Specifically, the timer 13 starts the time counter at the timing when the first pulse signal is input from the external interrupt circuit 12, stops the time counter at the timing when the next pulse signal is input, The value of the time counter (time count value) is output to the CPU 14.

  The CPU 14 (setting unit) performs overall control of communication operations of the communication device 1. Specifically, the CPU 14 generates transmission data and outputs it to the UART interface 11, or receives data input from the UART interface 11. Predetermined signal processing is performed. Further, the CPU 14 calculates the baud rate of the UART signal transmitted from the communication counterpart device 2 based on the time count value (time measurement result) input from the timer 13, and the calculated baud rate is set in the setting register of the UART interface 11. 11a has a baud rate automatic setting function set to 11a.

  Next, the operation of the communication apparatus 1 in the present embodiment configured as described above, in particular, the baud rate setting operation will be described in detail. First, before starting the description of the baud rate setting operation, the format of the UART signal as a premise thereof will be described. FIG. 2A shows the format of a UART signal transmitted and received between the communication device 1 and the communication partner device 2 during normal communication (after establishing a communication connection), and FIG. 2B shows the communication connection. The format of the UART signal transmitted from the communication partner device 2 to the communication device 1 at the time of establishment is shown.

  As shown in FIG. 2A, during normal communication, a UART signal including a start bit (1 bit), a data bit (8 bits), and a stop bit (1 bit) in one frame is transmitted to the communication apparatus 1 and a communication partner. It is transmitted to and received from the device 2. In the UART communication, it is defined that the start bit section is set to a low level (“0”) and the stop bit section is set to a high level (“1”).

  On the other hand, as shown in FIG. 2B, at the time of establishing the communication connection, the UART signal generated under the condition of “no parity, data = 00 hex”, that is, the start bit section is low level in one frame. The communication partner apparatus 2 transmits a UART signal in which the stop bit interval is set to a high level and the interval between the start bit and the stop bit is set to a low level. In this case, 9 bits are a low level section in one frame.

  As shown in FIG. 2B, the communication device 1 measures the time of the low level section in one frame of the UART signal transmitted from the communication partner device 2 when the communication connection is established, and based on the measurement result. To calculate the baud rate. FIG. 3 is a flowchart showing the baud rate setting operation of the communication device 1 when establishing a communication connection.

 As shown in FIG. 3, first, the external interrupt circuit 12 of the communication device 1 monitors the UART signal transmitted from the communication partner device 2 and determines whether or not a falling edge has been detected (step S1). . In this step S1, if “Yes”, the external interrupt circuit 12 outputs a high-level pulse signal to the timer 13 at the timing when the falling edge is detected, and the timer 13 at the timing when the pulse signal is input. The time counter is activated (step S2).

  Then, the external interrupt circuit 12 continues to monitor the UART signal transmitted from the communication counterpart device 2 and determines whether or not a rising edge has been detected (step S3). In the case of “Yes” in step S3, the external interrupt circuit 12 outputs a high level pulse signal to the timer 13 at the timing when the rising edge is detected, and the timer 13 times at the timing when the pulse signal is input. The counter is stopped (step S4). Here, the timer 13 outputs the time count value at that time to the CPU 14.

  Then, the CPU 14 calculates the baud rate of the UART signal transmitted from the communication counterpart device 2 based on the time count value input from the timer 13 (step S5). Specifically, the time count value is a value indicating the time of a low level section (9 bits section) in one frame in the UART signal shown in FIG. The baud rate can be calculated by dividing the reciprocal by 9. The CPU 14 sets the baud rate calculated in this way in the setting register 11a of the UART interface 11 (step S6).

  FIG. 4 is a timing chart showing the baud rate setting operation of the communication apparatus 1 described above. As shown in FIG. 4, at the timing when the falling edge of the UART signal is detected, a pulse signal is output from the external interrupt circuit 12 to the timer 13 to start the time counter, and thereafter, the rising edge of the UART signal At the detected timing, the pulse signal is output again from the external interrupt circuit 12 to the timer 13, the time counter is stopped, the baud rate is calculated by the CPU 14, and the baud rate is set in the setting register 11a.

  As described above, in the communication apparatus 1 of the present embodiment, the baud rate calculation accuracy is improved because the baud rate is calculated not only from the conventional start bit section but also from the time measurement result of the section over a plurality of bits. be able to. Further, in order to measure the time of the section, it is only necessary to provide the external interrupt circuit 12 for detecting the falling edge and the rising edge of the UART signal and the timer 13 for performing the time measuring operation, so that the circuit configuration is simplified. can do. That is, according to the communication apparatus 1 of the present embodiment, it is possible to achieve both improvement in baud rate calculation accuracy and simplification of the circuit configuration.

In addition, this invention is not limited to the said embodiment, The following modifications are mentioned.
(1) In the above embodiment, the case where the baud rate is calculated based on the time count value obtained by measuring only the low level section in one frame included in the UART signal transmitted from the communication partner apparatus 2 is exemplified. The CPU 14 may be provided with a function of calculating an average value of the baud rate based on the time count value obtained for each of the plurality of frames and setting the calculated average value of the baud rate in the UART interface 11. Thereby, the calculation accuracy of the baud rate can be further improved.

(2) In the above embodiment, the communication device 1 including the UART interface 11 as a communication unit that transmits and receives a serial signal including a start bit and an end bit in one frame is illustrated. However, a start bit and an end bit are included in one frame. Other interfaces may be used as long as they can transmit and receive serial signals. Further, the format of the UART signal is not limited to that shown in FIG. In particular, it is desirable that the low level section in one frame in the UART signal transmitted from the communication partner apparatus 2 to the communication apparatus 1 is longer when establishing the communication connection.

  DESCRIPTION OF SYMBOLS 1 ... Communication apparatus, 11 ... UART interface (communication part), 11a ... Setting register, 12 ... External interrupt circuit (detection part), 13 ... Timer (time measuring part), 14 ... CPU (Central Processing Unit: Setting part), 2 ... Communication partner device, 21 ... UART interface

Claims (4)

A communication unit for transmitting and receiving a serial signal including a start bit and an end bit in one frame;
A detection unit for detecting the start bit and the end bit included in the serial signal transmitted from a communication partner device;
A timing unit that starts a timing operation when the detection unit detects the start bit, and ends the timing operation when the detection unit detects the end bit;
A baud rate is calculated based on the time measurement result of the time measuring unit, and a setting unit that sets the calculated baud rate in the communication unit;
A communication apparatus comprising: Within the one frame, the start bit interval is set to low level, the end bit interval is set to high level, and the interval between the start bit and the end bit is set to low level. When sent from the other device,
The communication device according to claim 1, wherein the detection unit detects a falling edge of the serial signal as the start bit, and detects a rising edge of the serial signal as the end bit.   The setting unit calculates an average value of the baud rate based on a timing result of the timing unit obtained for each of a plurality of frames, and sets the calculated average value of the baud rate in the communication unit. The communication device according to claim 1 or 2.   The communication apparatus according to claim 1, wherein the communication unit is a UART (Universal Asynchronous Receiver Transmitter) interface.

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