In any program it is essential to move the data in the memory and in the CPU registers; there are a number of ways to do this: it can copy data in the memory to a number of register, from register to register, from a stack to a register, from a register to a stack, to transmit data to external devices in addition to vice versa.
This group of data is subject to rules and restrictions. The next are some of them:
*It is not potential to move data from a memory locality to another unswervingly; it is essential to first move the data of the origin locality to a register and then from the register to the destiny area.
*It is not possible to move a constant straight to a segment register; it first must be moved to a register in the CPU then to segment register.
It is feasible to move data blocks through the movs instructions, which copies a chain of bytes or words; movsb which copies n bytes from a region to another; and movsw copies n words from a locality to another. The last two instructions take the values from the distinct addresses by DS:SI as a set of data to move and ES:DI as the new localization of the
data.
To move data there are also structures identified batteries, where the data is introduced with the push instruction and are removed with the pop instruction.
In a stack the first data to be introduced is the last one we can take, this is, if in our program we utilize these instructions:
PUSH AX
PUSH BX
PUSH CX
To return the accurate values to each register at the moment of taking them from the stack it is essential to do it in the following sequence:
POP CX
POP BX
POP AX
For the contact with external devices the in command to read the information received from a port and the out command is used to send information to a port.
The out command’s syntax is:
OUT DX,AX
The in command’s syntax is:
IN AX,DX