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3-6 DM (Data Memory) Area
The DM area is divided into various parts as described in the following table. A
portion of UM (up to 3,000 words in 1,000-word increments) can be allocated as
Expansion DM.
Addresses User
read/write
Usage
DM 0000 to DM 0999 Read/Write Normal DM.
DM 1000 to DM 1999 Special I/O Unit Area
1
DM 2000 to DM 5999 Normal DM.
DM 6000 to DM 6030 History Log
DM 6100 to DM 6143 Link test area (reserved)
DM 6144 to DM 6599 Read only System Settings
DM 6600 to DM 6655 PC Setup
DM 7000 to DM 9999 Expansion DM
2
Note 1. The PC Setup can be set to use DM 7000 through DM 7999 as the Special
I/O Area instead of DM 1000 to DM 1999. Refer to
3-6-4 PC Setup
for de-
tails.
2. The UM ALLOCATION Programming Console operation can be used to al-
locate up to 3000 words of UM as Expansion DM.
Although composed of 16-bit words like any other data area, data in the DM area
cannot be specified by bit for use in instructions with bit operands. DM 0000 to
DM 6143 can be written to by the program, but DM 6144 to DM 6655 can be over-
written only from a Peripheral Device, such as a Programming Console or host
computer with LSS.
The DM area retains status during power interruptions.
Indirect Addressing 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, sup-
pose MOV(21) is performed with DM 0100 as the first operand and LR 20 as the
second operand. When this instruction is executed, the content of DM 0100 is
moved to LR 20.
Note Expansion DM cannot be used for indirect addressing.
It is possible, however, to use indirect DM addresses as the operands for many
instructions. To indicate an indirect DM address, :DM is input with the address
of the operand. With an indirect address, with content of this operand does not
contain the actual data to be used. Instead, it’s contents is assumed to hold the
address of another DM word, the content of which will actually be used in the
instruction. If :DM 0100 was used in our example above and the content of DM
0100 is 0324, then :DM 0100 actually means that the content of DM 0324 is to
be used as the operand in the instruction, and the content of DM 0324 will be
moved to LR 20.
MOV(21)
:DM 0100
LR 00
Word Content
DM 0099 4C59
DM 0100 0324
DM 0101 F35A
DM 0324 5555
DM 0325 2506
DM 0326 D541
5555 moved
to LR 00.
Indicates
DM 0324
Indirect
address
DM Area Section 3-6