The device connected to an in-out channel communicates directly with
memory through the Memory Buffer Register. At the completion of each
machine instruction, a check is made to see if the in-out channel has a
word for, or needs a word from, the memory. When necessary, a memory
cycle is taken to serve the channel. The operation is initiated by an
in-out command. The in-out transfer command indicates the nature of the
transfer. The left half of the In-Out Register must contain the
starting address of the transfer, and the right half must contain the
number of words to be transferred. If the Sequence Break System is
connected, the completion of the transfer will signal the proper
sequence. If no Sequence Break System is connected, the completion of
the in-out channel transfer sets a program flag.