For example, in BS mode, with 10 slaves having TX_PERMIT_LEN values of 3, 5, 7 ... 19, 21, the average value is 12.
In A mode, the default TX_PERMIT_LEN value for all slaves can be the same as the master's.
TX_PERMIT_LEN must be ≥ 1, and IDLE_WAIT_LEN must be ≥ 10.