IP Adapters User Manual

Table Of Contents

Publication 1734-UM016A-EN-P - October 2010

6 Configuration

Data Alignment

Some computing devices require data to be aligned on boundaries that are

proper for their data type. There are several alignment options available to

reduce or prevent shifting operations in the originator:

Byte Boundaries

Each node's I/O data is mapped at the next available byte. Byte data can

appear at any address.

Word Boundaries

If a node's I/O data is one byte in length, it is mapped at the next available

byte. Otherwise the previous data is padded so that the node's data starts on a

16-bit boundary.

Double Word Boundaries

If a node's I/O data is one byte in length, it is mapped at the next available

byte. If a node's data is two bytes in length, padding is added to ensure that it is

mapped to an even address. If a node's data is greater than 2 bytes in length,

padding is added to ensure that the data is mapped to a Double Word

boundary.

Fixed Boundaries

The fixed boundary allows you to choose the fixed "size per slot" that each

module occupies in the I/O data. Mapping size ranges from 1…24 bytes.

The alignment choices are independently selected for each direction; O → T

and T

→ O. If Fixed Boundaries are selected, the Size per Slot choice

determines how many bytes are reserved for each slot in the I/O packet. If the

size selected is larger than a module's data, that module's data is padded with

0's out to the size selected. If the size selected is smaller than a module's data,

that module's data is truncated at the size selected.

TIP

This does not mean that every slot occupies two bytes in the image.

Word data can only begin on even addresses, for example, 0, 2, 4, 8,

0xA, or 0xC.

TIP

This does not mean that every slot occupies 4 bytes in the image.

Double Word data and array data larger than 2 bytes in size must be

aligned on addresses ending in 0, 4, 8, and 0xC.