uint32_tbackofflimit:2;/*The Back-Off limit determines the random integer number (r) of slot time delays (512 bit times for 10/100 Mbps) for which the MAC waits before rescheduling a transmission attempt during retries after a collision. This bit is applicable only in the half-duplex mode. 00: k= min (n 10). 01: k = min (n 8). 10: k = min (n 4). 11: k = min (n 1) n = retransmission attempt. The random integer r takes the value in the Range 0 ~ 2000.*/