Emerson PaCSystems VersaMax Series, Руководство пользователя, Страница: 104 / 308

User Manual Chapter 9
GFK-1503F Jan 2020
Program Data 90
Chapter 9: Program Data
This chapter describes the types of data that can be used in an application program, and
explains how that data is stored in the VersaMax
TM PLC’s memory.
• Data memory references
• Retentiveness of data
• Using names and descriptions for program references
• System status references
• Time tick contacts
• How program functions handle numerical data
9.1 Data Memory References
The PLC stores program data in both bit memory and word memory. Both bit memory and
word memory are divided into different types with specific characteristics.
By convention, each type is normally used for a specific type of data, as explained below.
However, there is great flexibility in actual memory assignment.
Individual memory locations are indexed using alphanumeric identifiers called references.
The reference’s letter prefix identifies the memory area. The numerical value is the offset
within that memory area.
9.1.1 Word Memory References
Each word memory address (reference) is on a 16-bit word boundary. The PLC uses three
types of references for data stored in word memory.
%AI Normally used for analog inputs.
%AQ Normally used for analog outputs.
%R Registers are normally used to store program data in word format.
Word memory is represented below. The example below shows ten addresses. Each has 16
bits that together contain one value. The PLC cannot access individual bits in word memory.