Data reception apparatus and synchronizing signal detection method and program
To detect the Synch Field accurately and find the beginning of a frame in order to calculate the baud rate. A slave device is connected to a bus and receives a binary level signal on the bus transmitted from a master device. The slave device detects the signal level of the binary level signal and calculates the time of a first period and a second period when the binary level signal is at a low level, which respectively exist before and after the binary level signal is at a high level. When the ratio of the first period to the second period is not less than 11, the binary level signal that the device continues to receive after the second period is identified as the Synch Field. From the reciprocal number of the second period, the baud rate for the slave device to receive the binary level signal is calculated.
1 . A data reception apparatus that is connected to a bus and that receives a binary level signal on the bus comprising:
a signal detection unit that detects the signal level of said binary level signal;
a period calculation unit that calculates first and second periods when said binary level signal is at a second level, which are respectively detected before and after periods when said binary level signal is at a first level;
a comparison unit that calculates a ratio of said first period to said second period; and
a synchronization detection unit that identifies a binary level signal that follows the second period as a synchronizing signal when the ratio calculated by said comparison unit is not less than a predetermined value.
2 . The data reception apparatus as defined in claim 1 wherein said period calculation unit comprises a timer that measures a time interval between a first point when the signal level of said binary level signal changes from said first level to said second level and a second point when it changes from said second level to said first level, and a memory unit that outputs a time interval that has been already stored as said first period at said second point and that stores the time interval measured by said timer as said second period.
3 . The data reception apparatus as defined in claim 1 further comprising a baud rate calculation unit that calculates a baud rate for receiving said binary level signal based on said synchronizing signal.
4 . The data reception apparatus as defined in claim 3 wherein said baud rate calculation unit calculates said baud rate from the reciprocal number of said second period when the ratio calculated by said comparison unit is not less than said predetermined value.
5 . A synchronizing signal detection method wherein a data reception apparatus that is connected to a bus and that receives a binary level signal on the bus detects a synchronizing signal of the binary level signal, the method comprises:
calculating first and second periods when said binary signal is at a second level, which are respectively detected before and after periods when said binary signal is at a first level, and
identifying said binary level signal received after said second period as a synchronizing signal when the ratio of said first period to said second period is not less than a predetermined value.
6 . The synchronizing signal detection method as defined in claim 5 wherein a baud rate for receiving said binary level signal is calculated based on said synchronizing signal.
7 . The synchronizing signal detection method as defined in claim 6 wherein the reciprocal number of said second period is calculated as said baud rate.
8 . A program having a computer constituting a data reception apparatus that is connected to a bus and that receives a binary level signal on the bus execute the following processing steps:
a time processing in which a time interval between a first point when the signal level of said binary level signal changes from a first level to a second level and a second point when it changes from said second level to said first level is measured;
a processing in which a time interval that has been already stored in a memory unit is outputted for comparison at said second point and the time interval measured in said time processing is stored in said memory unit;
a comparison processing in which a ratio of a time interval that has been already stored in said memory unit to a time interval measured in said time processing is calculated; and
a detection processing in which said binary level signal being received thereafter is detected as a synchronizing signal when the ratio calculated in said comparison processing is not less than a predetermined value.
9 . The program as defined in claim 8 having the computer further execute a baud rate calculation processing in which a baud rate for receiving said binary level signal is calculated based on said synchronizing signal.
10 . The program as defined in claim 9 wherein said baud rate is calculated from a reciprocal number of the value of the time interval measured in said time processing when the ratio calculated in said comparison processing is not less than said predetermined value in said baud rate calculation processing.