Control register of 8257

The processor, in active state writes to the Control register of 8257 to configure its working purpose. To find out the status of 8257, the processor reads status register of the processor. The control register is of length 8-bits which is only read by the processor but not read. It is only selected when CS* is 0, A3-0 is 1000, and IOW* is 0.

Intel calls the control register 8257 normally the mode set register by as it sets the mode of operation of 8257.

AULD1 = Enable auto load
0 = Disable auto load
TCS1 = Stop DMA transfer if TC reached
0 = No automatic stop of DMA on occurrence of TC
EXWR1 = Enable extended write
0 = Enable extended write
RTPR1 = Enable rotating Priority
0 = Disable rotating Priority
ECHn1 = Enable DMA Channel n (n = 0-3)
0 = Disable DMA Channel n