I read in the PROFIBUS PA specs that the max length of EACH spur is 30/60/120 m, but in PROFIBUS DP we have defined the spur length parameter as TOTAL spur length. Can you explain?
Because the baudrate is relatively low with PROFIBUS PA, spur lines are allowed to be long without disturbing the data communication and we can assign a fixed maximum length per spur / per device. With PROFIBUS DP it is a different story; the high baudrate limits the spur line length. If we would fix the maximum length per device, it would only be 20 cm per spur for 32 devices and that would not make sense. To solve this we define it as a total sum of all spurs together so that the end-user has more flexibility, because not all devices require a spur line.
