Auto allocated PDO COB-ID with too high priority

When additional PDOs are enabled in a slave (PDO 5 and higher), COB-ID is automatically allocated. The values start with 2 and go upto 0x7F. Then next used free area is 0x680 upto 0x700.

Since a low COB-ID has a higher priority on bus, these PDOs would have a higher priority than SYNC, EMCY and TIME telegrams.

Auto allocation should start with higher numbers, to lower the probability of such configurations: first use 0x680-0x700, then 2-0x7F.