Memory Map
With any PLC system, you generally have many different types of information to process.
This includes input device status, output device status, various timing elements, parts counts,
etc. It is important to understand how the system represents and stores the various types of
data. For example, you need to know how the system identifies input points, output points,
data words, etc. The following paragraphs discuss the various memory types used in the
DL205 CPUs. A memory map overview for the DL230, DL240, DL250–1 and DL260
CPUs follows the memory descriptions.
Octal Numbering System
All memory locations or areas are numbered in Octal
(base 8). For example, the diagram shows how the
octal numbering system works for the discrete input
points. Notice the octal system does not contain any
numbers with the digits 8 or 9.
Discrete and Word Locations
As you examine the different memory types, you’ll
notice two types of memory in the DL205, discrete
and word memory. Discrete memory is one bit that
can be either a 1 or a 0. Word memory is referred to as
V memory (variable) and is a 16-bit location normally
used to manipulate data/numbers, store data/numbers,
etc. Some information is automatically stored in V-
memory. For example, the timer current values are
stored in V-memory.
V–Memory Locations for Discrete Memory Areas
The discrete memory area is for inputs, outputs, control relays, special relays, stages, timer
status bits and counter status bits. However, you can also access the bit data types as a V-
memory word. Each V-memory location contains 16 consecutive discrete locations. For
example, the following diagram shows how the X input points are mapped into V-memory
locations.
These discrete memory areas and their corresponding V-memory ranges are listed in the
memory area table for the DL230, DL240, DL250–1 and DL260 CPUs in this chapter.
DL205 User Manual, 4th Edition, Rev. B
3–37
Chapter 3: CPU Specifications and Operations
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