Because the IR must use the bus to copy the value of X into the MAR, before
the data at location X can be placed into the MBR, this operation requires two bus
cycles. Therefore, these two operations are on separate lines to indicate they cannot
occur during the same cycle. However, because we have a special connection
between the MBR and the AC, the transfer of the data from the MBR to theAC can
occur immediately after the data is put into the MBR, without waiting for the bus.
Store X
This instruction stores the contents of the AC in memory location X: