Eric is right. K2M300 represents the group of eight bits with head address M300 or from m300 to m307 (The value next to k in k2m300, which is 2, multiplied by 4 to get 8 bits...thus k1m300 4 bits from m300 to m303, k3m300 12 bits from m300 to m311, k4m300 16bits from m300 to m315). K2M300 in your question is the source data to be written to your buffer memory address k16 of your special expansion block with block position k0 (the first block after the cpu to the right).