In general, upper 4 bits of Machine Instruction are assigned to an OP(eration) code and lower 12-bits the Operand which points to a location of the memory. Here we look at "ROL" (Rotate Left G register) instruction in detail.

Machine Instruction: 1101 0000 0000 0000
Assembly Instruction: ROL
Description: Shift G register 1 bit to left with old G[15] back to new G[0]
The sequence of operations to be performed in Fetch Cycle:

Subcycle	HDL	Note
T6	X<-G	copy G to X Register in ALU
T7	G<-ROL(X)	Load ROL(X) in ALU to G register