Control system for duplex communications channels

Abstract: This system is applicable to channels that use packet, frame or message protocols, for which a half-duplex communications controller (1) is connected to a multiplexer (2) which, in turn, is connected to two different clock circuits (3, 4), to provide the controller with a working frequency in the reception mode and another working frequency in the transmission mode. The system includes a buffer memory (11) in which the data to be transmitted are stored at a rate much higher than that at which they are transmitted to the line, these data being transferred to a serializer (15) which delivers the data to the line (8) through a transmission interface (16) at the line transmission rate. The system is normally in the reception mode and changes from this state when the transmission operation is desired, after having verified that no reception is taking place.

Description: OBJECT OF THE INVENTION This invention, as stated in the title of this technical description, consists of a control system for duplex communications channels which uses a single half-duplex communications controller for both directions of transmission. An example of such half-duplex communication controllers may be found in U.S. patent No. 4,177,451. The invention considered here has the object of controlling a duplex communications link in which well-defined messages, packets or frames are used, at moderate or low signalling rates (19.2 kbit/s and lower). In accordance with the invention, and contrarily to what is taught by the above U.S. patent No. 4,177,451, the half-duplex communications controller, in transmission mode, works at a rate much higher than that of line transmission and at that of the half-duplex communications controller in reception mode. BACKGROUND TO THE INVENTION Duplex communications channels with simple communications protocols have traditionally been controlled with duplex control elements. As an example, consider the case of the circuits termed USART (Universal Synchronous Asyncronous Receiver Transmitter), among which the type 2651 is an industry standard (see "Philips Integrated Circuits Book IC 14N", 1985, pages 993 to 1006), which allow handling of communications protocols of the start/stop type and of the synchronous transmission type (including the IBM BiSync). When the protocol is complex, as happens with bit-oriented protocols, e.g. HDLC, duplex controllers, expensive and complex in their operation, or else two half-duplex controllers, simpler and less expensive, one for each direction of transmission, can be used. At present, duplex communications controllers are available on the market that permit control of duplex communications channels with a wide range of protocols, such as the types SCN2652 (see "Philips Integrated Circuits Book IC 14N", 1985, pages 563 to 582), or the I82530 (see "Intel Microcommunications Bandbook", 1986, pages 9.83 to 9.110). These controllers require a complex control process governed by the associated microprocessor and, in addition, they are very expensive. CHARACTERIZATION OF THE INVENTION The object of the invention is to create a control system for duplex communication channels, making use of a single half-duplex communications controller, for which the invention is characterised in that the half-duplex communications controller is connected to a multiplexer which, in turn, is connected to two different clock circuits, with the object of providing it with a working frequency in reception mode and another working frequency in transmission mode; in that the half-duplex communications controller is connected, through a first control element, to a buffer memory in which the data are stored at a rate much higher than that at which they are transmitted to the line, and the output of which is connected to a serialiser circuit which delivers the data on line, through a transmission interface, at the line transmission rate; and in that the half-duplex communications controller is connected, through a second control element, to a reception interface that is connected to the line, in order to effect the reception at the line reception rate. Reception takes place directly through the reception interface at the line reception rate. On the other hand, to effect transmission, the data for sending are stored in the buffer memory at a rate much higher than the rate at which they are transmitted to line, the data being transferred to a parallel register at a rate eight times less than the line transmission rate. The data are then sent to a new serial-parallel register, from which they are transmitted on line through the transmission interface at the line transmission rate. Next, to facilitate a better understanding of this description and forming an integral part thereof, a single figure is attached, which shows the block diagram of the system of the invention. BRIEF DESCRIPTION OF THE FIGURES Figure 1, shows the block diagram of the system object of the invention. DESCRIPTION OF THE INVENTION The invention is based on a half-duplex communications controller which is supplied with a clock signal at a frequency that depends on whether it is working in the transmission mode or in the reception mode. The half-duplex communications controller normally works in the reception mode, receiving a clock signal that is suitable for the line reception rate; it changes for transmission mode operation when there is something to be transmitted and there is no information being received from the line. In the latter case, it is supplied with a clock signal as fast as the operation of the controller permits, and the information is passed into a buffer memory. From this memory, the information is read at the line transmission rate and transmission to the line is carried out in a continuous manner. In this way, a quasi-duplex operation is achieved, the approximation to true duplex operation thus increasing as the ratio between the transmission mode clock signal and the reception mode clock signal increases. Following, and making reference to the figure mentioned above, a description of the invention, which carries out the functions specified, is given. Normally, the system works in the reception mode, for which the half-duplex communications controller 1 keeps the RTS signal high (on), and consequently the clock signal selected through multiplexer 2 corresponds to the line reception rate, as generated by the reception clock circuit 3. When transmission operation is desired, the half-duplex communications controller 1 changes the RTS signal to low (off) and, consequently, through multiplexer 2 the clock signal selected is that corresponding to the storage rate for data to be transmitted in the buffer memory 11, generated by the fast clock circuit 4. The half-duplex communications controller 1 also generates the I/O control signal which is synchronised with the CTS signal produced by the delay circuit 5, the function of which is to delay the RTS signal for the time required by the half-duplex communications controller to change from the reception to the transmission state. The I/O control signal is applied to the control elements 6 and 7. If the I/O control signal is high (on), only control element 7 is activated, which permits the transfer of the information coming from line 8, through reception interface 9, to input 10 of the half-duplex communications controller 1. If the I/O control signal is low (off), only the control element 6 is activated, which permits the transfer of the information to be transmitted to the buffer memory 11. To allow the correct operation of the buffer memory 11, this latter is connected to a third control element 12 at the inputs to which is received the CTS signal and the signal coming from the fast clock circuit 4, termed the CKRR signal, which enable the writing of the data to be transmitted in the buffer memory 11 at the rate corresponding to the fast clock 4. Once the message to be transmitted has been transferred to the buffer memory 11, the controller resets the I/O and RTS signals to the high (on) state, thus returning to the reception mode. The information stored in the buffer memory 11 is loaded in parallel, byte by byte, into the serialiser 15, for which reason the memory is connected to the line transmission clock circuit 13 through a divide-by-eight frequency divider 14, such that the memory is read at a rate eight times less than the line transmission rate. The serialiser 15 consists of two eight-bit registers, such that the first of these receives in parallel the information coming from the buffer memory 11 and sends it with the appropriate timing to the second register which, in turn, converts it to serial form controlled by the CKTRL signal from the line transmission clock 13, for its transmission to line 8 through the transmission interface 16. As can be gathered from the description up to this point, when the half-duplex communications controller 1 is in the transmission mode, all information being received from the line is lost. Nonetheless, if the value of the ratio between the frequency of the CKRR signal from the fast clock 4 and that of the CKRL signal from the reception clock 3 is high, e.g.≧100, and taking into account that the flow of information received is not continuous due to the packet or frame formation process in the remote controller, and to the confirmation process of these, the percentage of lost frames and consequently to be retransmitted is very low. From all the foregoing, it can therefore be deduced that in the reception mode, the information is received through the reception interface 9, and transferred to the half-duplex communications controller 1 through the control element 7. During this phase, the half-duplex communications controller 1 works with the CKRL clock signal, generated by the reception clock circuit 3 and selected by means of the multiplexer 2. In the transmission mode, the half-duplex communications controller 1, once it has checked that it is not receiving information from the line, starts to work with the CKRR clock signal, generated by the fast clock circuit 4 and selected by means of multiplexer 2, and sends the information required to be transmitted to the buffer memory 11. Simultaneously, the buffer memory 11 is read in parallel and loaded into the serialiser 15, then passing to the transmission interface 16 for sending on line 8.

Claims: CONTROL SYSTEM FOR DUPLEX COMMUNICATION CHANNELS on a transmission line (8), applicable to duplex channels that use protocols with well-defined frames, packets or messages, characterised in that: a half-duplex communications controller (1) is connected to a multiplexer (2) which, in turn, is connected to two different clock circuits (3 and 4) with the object of providing it with a working frequency in reception mode and another working frequency in transmission mode; the half-duplex communications controller (1) is connected, through a first control element (6), to a buffer memory (11) in which the data are stored at a rate much higher than that at which they are transmitted to the line (8), and the output of which is connected to a serialiser circuit (15) which delivers the data on line, through a transmission interface (16), at the line transmission rate; and the half-duplex communications controller (1) is connected, through a second control element (7), to a reception interface (9) that is connected to the line (8), in order to effect the reception at the line reception rate. CONTROL SYSTEM FOR DUPLEX COMMUNICATIONS CHANNELS according to claim 1, characterised in that the control elements (6, 7) are connected to the half-duplex communications controller (1) over a common line (I/O) which causes only one of the control elements (6, 7) to be activated depending on whether the system is in the reception or in the transmission mode, and over another common line (10) that is used to receive the information from the line (8) and to send to the buffer memory (11) the information to be transmitted. CONTROL SYSTEM FOR DUPLEX COMMUNICATIONS CHANNELS according to claim 1, characterised in that the half-duplex communications controller (1) is also connected to a delay circuit (5) that delays the working mode selection signal ( RTS ) for the time necessary for the half-duplex communications controller (1) to change from the reception to the transmission state. CONTROL SYSTEM FOR DUPLEX COMMUNICATIONS CHANNELS according to claim 1, characterised in that the buffer memory (11) is also connected to a third control element (12) that governs writing data in the memory at the rate of the fast clock (4), and to a line transmission clock circuit (13), through a divide-by-eight frequency divider (14), which governs the read signal and consequently the transfer of data from the buffer memory (11) to the serialiser (15). CONTROL SYSTEM FOR DUPLEX COMMUNICATIONS CHANNELS according to the preceding claims, characterised in that the serialiser circuit (15) includes a parallel load register that is operated by the signal from the divide-by-eight divider (14) and a parallel-load and serial-output register operated by the (CKTRL) signal from the line transmission clock (13), the transmission to line (8) taking place at the line transmission rate. CONTROL SYSTEM FOR DUPLEX COMMUNICATIONS CHANNELS according to preceding claims, characterised in that the half-duplex communications controller (1) is normally in the reception mode, and changes this state when transmission operation is desired, after having verified that it is not receiving information from the line (8).

Inventors: HITA DE LA TORRE CARLOS, HITA DE LA TORRE, CARLOS
Applicants: ALCATEL NV, ALCATEL N.V.
Application year: 1989
Main classification: H04L5
IPC codes: H04L5