1. Field of the Invention
This invention relates to a data reception device and data reception method used to receive data that has been transmitted in accordance with certain data-transfer Standards in the form of a packetized differential signal, and electronic equipment that includes such a device.
2. Description of Related Art
A differential signal is a paired signal consisting of a positive-polarity signal and a negative-polarity signal having a waveform that is the inverse thereof. When signal lines for such positive-polarity and negative-polarity signals are connected to data reception device designed to receive this differential signal, it could happen that these signal lines are connected to a terminal that is previously designated for a positive-polarity signal and a terminal that is previously designated for a negative-polarity signal the wrong way round. If the data reception device identifies the polarities of these two signals incorrectly, it will not be possible for the receiver to read the data correctly.
It is therefore desired that this data reception device determines whether or not the polarities of the two signals received as a differential signal have been identified correctly, and also automatically correct the polarities it they have been identified incorrectly.
One prior-art technique used by data reception devices for correctly identifying the polarities of these two signals is a method that uses an idle pulse at the end of the packet to determine the polarities. An idle pulse has a long pulse width at a high level. Thus, if this prior-art technique determines that the long pulse at the end of a packet is at a low level, it determines that the terminals for the positive-polarity and negative-polarity signals have been connected reversed.
However, this method of using an idle pulse at the end of a packet for determining the polarities has disadvantages, as described below.
In order to detect this long idle pulse at the end of the packet, it is necessary to sample the idle pulse. However, there is no clock component of the packet at the rear part of this idle pulse, making it difficult to regain synchronization.
To identify this idle pulse, the circuitry of the section within the data reception device that receives the differential signal must have a certain degree of accuracy. However, the circuitry of the reception section would become complicated if it is required to have a certain degree of accuracy when receiving and decoding a signal containing jitter. It is therefore difficult to provide such a circuit that is simple and can be manufactured with a high yield.
In a data reception device that manipulates the waveform of the received signal and uses a regenerated data signal for decoding, it is possible that this method of using the regenerated data signal to identify the idle pulse will become difficult. This is because the regenerated data signal does not necessarily reproduce the information relating to the waveform of the received signal accurately.
These problems with accuracy in the signal used for the determination make it difficult to implement this method of determining polarities using the idle pulse at the end of the packet.