The multiplexer provides the system control signals as long as the 80X86 is in control of the system.During a DMA action (AEN=1), latches A and C are disabled along with multiplexer (E).

• 在一个DMA活动周期中，多路复用器会提供系统控制信号，只要此时80X86处于系统的控制下，而且锁存器A，C会随着多路复用器(E)变为无效。