# BASEstartm Open DAS
for Allen-Bradley Data Highwaytm
on Tru64tm UNIX
Installation and User's Guide

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# 3.3 Addressing Syntax and Supported Data Types

Data types are defined at the device and application levels. The device data type is referred to as the MMS data type. The MMS data type is mapped to an application data type.

Data types can be either simple or complex. Simple data types are native to the OMNI environment. Complex data types are divided into either arrays or structures. Complex data types must be created by a user before they can be used in defining data points or variables.

The following sections describe the supported data types and addressing syntax for each of the supported PLC families.

## 3.3.1 PLC-2 Addressing Syntax and Supported Data Types

Figure 3-1 shows the structure of a legal address for the PLC-2 family.

Figure 3-1 General PLC-2 Address Format

Table 3-7 shows examples of valid addresses for the PLC-2 family.

Table 3-7 Example PLC-2 Data Types
Example Address | MMS Type1 | Description
--- | --- | ---
377 | UNSIGNED_16 | Word 377 octal including status bits 2
20 | BCD3 3 | Word 20 octal 2
1777/17 | BIT_STRING | Bit 17 octal of word 1777 octal 2
33 | Array of 10 BCD3 | Ten words beginning at word 33 octal

1Arrays are supported. Structures are not supported. Variable size arrays are not supported.
2Control bits should be treated as read only and modified only under PLC program control. Modifying these bits from a computer can give unpredictable results.
3The number must be a valid BCD number from 0-999. Status bits are cleared.

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