It will copies bits from device (or devices), in your case D266 to output device (or devices), in your case K4M229. Last number K7, represents how many consecutive devices will be copied. D266 is 16 bit device, so for that reason there is K4M229 (4 nibbles, one nibble is 4 bits, so 4x4=16 bits).
This exact command will copy, 112 bits from D266 - D332, to memory bits from M229 to M340.