Managing and Controlling the GPIB
Five GPIB hardware lines manage the flow of information across the bus. These lines are referred to as interface management lines or control lines.
| Line | Description |
| ATN (attention) | The Controller-In-Charge (CIC) drives this line to indicate the type of message present on the data lines. ATN is asserted when the message is a command from the CIC; it is unasserted when the message is a data byte from a Talker. |
| IFC (interface clear) | The System Controller drives the IFC line to initialize the bus and make itself CIC. When IFC is asserted, all devices return to a known, quiescent state. |
| REN (remote enable) | The System Controller drives the REN line to place devices in remote or local program mode. |
| SRQ (service request) | Any device can assert the SRQ line to asynchronously request service from the Controller-In-Charge. SRQ remains asserted until the device is serial polled. The CIC should monitor the SRQ line, poll the device, and determine the type of service that the device needs. |
| EOI (end or identify) | If a device uses the EOI line to mark the end of a data message, it asserts EOI along with the last byte of data. A Listener stops reading data when EOI is asserted. The Controller also asserts the EOI line when it conducts a parallel poll. |