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Ethernet Communications Modules, 3rd Edition, Rev. D
4–6
Chapter 4: RLL Programming for Communications
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Addressing the Different Memory
Some data types are inherently 16 bits long, for example timer and counter current values.
Other data types are 1 bit long, for example: discrete inputs and outputs. Word-length and
bit-length data are mapped into Word Memory, also known as V-memory, which allows you to
address any of the different memory types as 16-bit words.
Bit Memory
Bit memory can be addressed in Read and Write instructions by the name of the first bit of any
byte. If your second LD instruction contains the constant K8, eight bytes will be transmitted. If
you use C0 in your RX or WX instruction, you will transmit the eight bytes from C0 through
C77.
Word Memory and Aliases
In the example below, V40600 is the V-memory designation for the sixteen bits from C0
through C17. Aliases are a convenient substitute for V-memory designations, and can be
used interchangeably in Read and Write instructions. VC0 is the alias for V40600. Either
nomenclature addresses the same 16 bits.
The alias is simply the name of the first bit in a group of sixteen bits, with V added as a prefix.
For example, VC0 represents the 16 bits beginning with C0. Word Memory, Bit Memory and
Aliases all use the octal numbering system.
The following Write routines are all equivalent.
Direct
SOFT gives you the flexibility to identify
the responding PLC’s memory area in three different ways, as shown below.
C1 C2 C3 C4 C5 C6 C7 C10 C11 C12 C13 C14 C15 C16 C17 C0
Word Memory Address V40600
= VC0 (Alias)
V40601 = VC20
V40602 = VC40
V40603 = VC60
C74 C73 C72 C71 C70 C67 C66 C65 C64 C63 C62 C61 C60 C75 C76 C77
C57 C56 C55 C54 C53 C52 C51 C50 C47 C46 C45 C44 C43 C42 C41 C40
C37 C36 C35 C34 C33 C32 C31 C30 C27 C26 C25 C24 C23 C22 C21 C20
LD
K114
LD
K8
LDA
O40600
WX
C100
LD
K114
LD
K8
LDA
O40600
WX
VC100
LD
K114
LD
K8
LDA
O40600
WX
V40600