MVI is used to move a
one byte immediate constant to a field in storage. Operand 1 denotes the field in main storage, while the second
operand is coded as a self-defining term
that gets assembled as a one byte immediate constant (II2) in the
second byte of the object code. Only
the first byte of Operand 1 is affected by the move.
As an example, consider the following code,
MVI FIELDA,X’C1’
...
FIELDA DC X’123456’
After execution, FIELDA
contains X’C13456’. Only the first byte
of the field is altered by the immediate instruction.
The following example
illustrates how an MVI instruction
might be processed by the assembler.
LOC
OBJECT CODE
000F12
92F4C044
MVI CUSTCODE,C’4’
...
001028 CUSTCODE
DS CL1
In the example above, the
op-code for MVI is x’92’, the self-defining term C’4’ is assembled as
the one byte hexadecimal constant x’F4’, and CUSTCODE is translated into the
base/displacement address C044.
Some Unrelated MVI’s:
J
DC C’ABC’
MVI J,C’X’ J = C’XBC’
MVI J,C’B’ J = C’BBC’
MVI J,C’5’ J = C’5BC’
MVI J,X’F5’ J = C’5BC’
MVI J,197 J = C’5BC’
MVI J,=C’5’ ASSEMBLY ERROR - OPERAND 2 NOT A SELF-DEFINING
TERM
MVI J(1),X’C5’ ASSEMBLY
ERROR - LENGTH SPECIFICATION NOT
ALLOWED IN
OPERAND 1