1. Field of the Invention
The present invention relates to a received data compensating device provided between a receiving circuit constituting a physical layer and a processing device utilizing received data and having the function of recovering the received data.
2. Description of the Related Art
FIG. 8 shows a diagram showing a structure of a conventional received data compensating circuit. As shown in FIG. 8, a received data compensating device 100A is provided in a rear stage of a receiving IC 200 constituting a physical layer and comprises a preprocessing unit 1 and a check unit 2 in this example. The receiving IC 200 is mounted on a printed wiring board (PWB) and the received data compensating device 100A can be properly constituted by an ASIC, an FPGA or a microcomputer. An AD485 adapter for an analog device can also be used for the receiving IC 200.
In FIG. 8, a digital signal acquired through the receiving IC 200 from a communicating transmission line is transferred to the received data compensating device 100A. The preprocessing unit 1 has a filtering function and a sampling function. An example of the sampling circuit to be used herein is shown in FIG. 9. This circuit has already been disclosed by the applicant based on Japanese Patent Application Laid-Open No. 2004-221905.
As shown in FIG. 9, the sampling circuit comprises three D-type flip-flops DFF1 to DFF3 which are cascade connected to each other, a first selector SEL1 disposed in a rear stage of DFF1 to DFF3, a D-type flip-flop DFF4 disposed in a rear stage of SEL1, a second selector SEL2 disposed in a rear stage of DFF4, and a D-type flip-flop DFF5 disposed in a rear stage of SEL2. The sampling circuit serves to monitor the Q outputs of the D-type flip-flops DFF1 to DFF5 and to give switching signals S1 and S2 to the first and second selectors SEL1 and SEL2 based on the Q outputs, thereby restoring a digital signal including various noise components as shown in FIGs. 10A-10H.
The check unit 2 of FIG. 8 serves to check a reliability of data in a frame format of a protocol such as a CRC, a parity, a stop or a coding rule or to detect an error. Furthermore, the check unit 2 also carries out decoding in the case in which a transmission line is coded. Compensated and received data (CD) passing through the check unit 2 are transmitted to the data processing device together with a check result signal S1 and are thus utilized (refer to, for example, Japanese Patent Application Laid-Open No. Hei 5-130151).
In such a conventional received data compensating device, however, a filtering circuit included in the preprocessing unit 1 is fixed to have one characteristic. Accordingly, such a PLC can be difficult to use in connecting a master unit to a slave unit.
More specifically, in the PLC system of this type, various wiring configurations such as a digichain, a multidrop, a branch and a start are mixed on a communicating path thereof. In addition, various transmission media (electric cables and connectors having different characteristics) are used. Consequently, a reflecting and damping state of a signal in a transmission line is varied. In the case in which this signal is received by the filtering circuit fixed to have one characteristic, a communication wiring specification such as a wiring length and the number of connections is more reduced than that in the case in which the wiring configuration and the transfer medium correspond. In order to solve this problem by an enhancement in a wiring performance, it is necessary to prepare an IC (including one filtering circuit) and an apparatus to be provided in a plurality of formats for each cable and wiring configuration irrespective of the device having the same function. For this reason, costs for development and management are increased.
The present invention has been made by taking note of the conventional problems and has an object to provide a received data compensating device capable of carrying out a wide application through a single device for a transmission line including various wiring configurations and transmission media.
Other objects, functions and advantages of the present invention will be easily understood by the skilled in the art by referring to the following description of the specification.