H

half-duplex

A communication link in which data transmission is limited to one direction at a time.

half slot addressing

See 1/2-slot addressing.

hexadecimal

The integer values displayed and entered in base 16 (that is, each digit represents 4 bits), prefixed with a "16#," and padded out to the length of the BOOL or integer (1, 8, 16, or 32 bits). Every group of 4 digits is separated by an underscore for legibility when displayed.

high byte

Bits 8 through 15 of a word.

High Integrity Add-On Instruction

A standard or safety Add-On Instruction that has a Signature, which means it has been sealed to prevent changes to the logic and definitions (sometimes referred to as a “sealed AOI”).

When an instruction is sealed, you can perform only the following actions:

1. Remove the Add-On Instruction signature.

2. Create signature history entry.

3. Add-on instruction copy operations (definition, invocations, documentation, signature, signature history).

4. Delete the Add-On Instruction.

5. Overwrite the Add-On Instruction via paste or import.

high nibble

The 4 most significant bits of a byte.

home position

A reference position for all absolute positioning movements usually defined by a home limit switch and encoder marker. It is normally set at power up and retained as long as the control system is operational.

homing

A method of calibrating an axis to a known position. It usually involves moving an axis to a physical position that can be verified with external sensors and inputs. The system then assigns a predefined position to the axis in this position.

homing sequence

Used to specify whether a home limit switch and/or the encoder marker would be used to locate the axis to a known position (when the Homing mode is active). The sequence types can include: immediate setting of position, moving until an external switch is triggered, moving until the motor’s internal marker is triggered, or using both an external switch and then the internal marker.

host name

The host name is the unique name that identifies a computer on a network.

On the Internet, the host name is in the form comp.xyz.net. If there is only one Internet site, the host name is the same as the domain name.

One computer can have more than one host name if it hosts more than one Internet site (for example, home.xyz.net and comp.xyz.net). In that case, home and comp are host names and xyz.net is the domain name.

Valid characters consist of:

Examples of legal host names include:

Examples of illegal host names include: