Omron SYSMAC CV Series Operation Manual page 81

DM and EM Areas
Indirect Addressing
Although composed of 16 bits just like any other word in memory, DM and
EM words cannot be specified by bit for use in instructions with bit-size oper-
ands, such as LD, OUT, AND, and OR, nor can DM words be used with the
SHIFT instruction.
The DM and EM Areas retain status during power interruptions.
Normally, when the content of a data area word is specified for an instruction,
the instruction is performed directly on the content of that word. For example,
suppose CMP(020) (COMPARE) is used in the program with CIO 0005 as
the first operand and D00010 as the second operand. When this instruction
is executed, the content of CIO 0005 is compared with that of D00010.
It is also possible, however, to use indirect DM and EM addresses as oper-
ands for instructions. If *D00100 is specified as the data for a programming
instruction, the asterisk in front of D indicates that it is an indirect address
that specifies another which contains the actual operand data. Likewise, EM
indirect addressing is indicated by an asterisk in front of the E, *E. When ad-
dressed indirectly, the content of *D00100 can be read as either BCD or
binary (hexadecimal) data, depending on the PC Setup for indirect addres-
sing.
If the PC Setup define the content of a *DM (or *EM) address as BCD, the
number indicates another DM (or EM) address. If the contents of the *DM
address are not BCD, a *DM BCD error will occur, and an error flag, A50003,
will be turned ON. Because only the last four digits of the final address can
be specified in one word, the range of possible BCD numbers is #0000 to
#9999, and the range of DM addresses that can be addressed indirectly is
D00000 to D09999.
If the content of D00100 is #0324, then *D00100 indicates D00324 as the
word that contains the desired data, and the content of D00324 is used as
the operand in the instruction. The following shows an example of this with
the MOVE instruction.
(030)
MOV *D00100
If the PC Setup define the content of a *DM address as binary, the number
indicates a PC memory address. The range of possible binary numbers,
$0000 to $FFFF, allows all memory areas, including EM, to be indirectly ad-
dressed.
wIf, in this case, the content of D00100 is $0324, then *D00100 indicates PC
memory address $0324, which is CIO 0804 in the SYSMAC BUS/2 Area, as the
word that contains the desired data, and the content of CIO 0804 is used as the
operand in the instruction. The following example shows this type of indirect ad-
dressing with the MOVE instruction.
Word
A090
D00099
D00100
Indirect
D00101
address
D00324
D00325
D00326
Section 3-11
Content
4C59
0324
Indicates
F35A
D00324.
5555
2506
5555 moved
to A0090.
D541
69