COMMUNICATION SYSTEM COMPRISING A DATA BUS AND A PLURALITY OF USERS CONNECTED TO SAID BUS, AND A METHOD FOR OPERATING SUCH A COMMUNICATION SYSTEM

摘要

The present invention relates to a communication system (1) comprising a data bus (2) and several subscriber nodes (3, 4) connected to the data bus (2), and to a method for operating such a communication system (1). Data frames (10) for data transmission each comprise a data field (14) and/or a control field (13) and a test sum field (15). A subscriber (3) has a high-precision clock generator (5) (such as precise quartz, MEMS resonator, and the like), and the remaining subscribers (4) have a clock generator (7) (such as an RC oscillator or imprecise quartz) having lower precision. During the operation of the communication system (1), calibration messages are present at the data bus (2), and the subscribers (4) having the imprecise clock generator (7) receive a calibration message. The subscribers (4) having the imprecise clock generator (7) calibrate the imprecise clock generator (7) for a system clock pulse (6) of the data bus (2), while taking information contained in the received calibration message into consideration. In order to expedite the calibration of such a communication system (1), and simultaneously save bandwidth on the data bus (2), it is proposed to use arbitrary messages transmitted via the data bus (2) as calibration messages for calibrating the system (1). For the calibration, a spacing (NOPN) between an edge (40) in the data field (14) or in the control field (13) of a received data frame (10) and another edge (41) in a field (13; 14; 15) of the received data frame (10) is measured in oscillator periods (8). The number (NB) of bits between said two edges (40, 41) is counted, and a clock pulse divider (9), which generates a system clock pulse (6) of a data bus protocol control system of the subscriber (4) to be calibrated, is to be set such that a system clock pulse period is NOPN/NB NTQ oscillator periods (8) long.