National Instruments GPIB-COM - page 52

Operation of the GPIB Appendix C

GPIB-COM User Manual C-4 © National Instruments Corporation

DAV (data valid)

DAV tells when the signals on the data lines are stable (valid) and can be accepted safely by

devices. The Controller drives DAV when sending commands, and the Talker drives it when

sending data messages.

The way in which NRFD and NDAC are used by the receiving device is called the Acceptor

Handshake. Likewise, the sending device uses DAV in the Source Handshake.

Interface Management Lines

Five lines are used to manage the flow of information across the interface.

ATN (attention)

The Controller drives ATN true when it uses the data lines to send commands and false when it

allows a Talker to send data messages.

IFC (interface clear)

The System Controller drives the IFC line to initialize the bus to become Controller-In-Charge.

REN (remote enable)

The System Controller drives the REN line, which is used to place devices in remote or local

program mode.

SRQ (service request)

Any device can drive the SRQ line to asynchronously request service from the Active Controller.

EOI (end or identify)

The EOI line has two purposes. The Talker uses the EOI line to mark the end of a message string.

The Active Controller uses the EOI line to tell devices to identify their responses in a parallel poll.

Contents

Main Page Page FCC/DOC Radio Frequency Interference Compliance Preface Introduction to the GPIB-COM Organization of This Manual Related Documents Abbreviations Used in This Manual Contents Page Figures Tables Section One Introduction GPIB-COM Characteristics What Your Kit Should Contain Optional Equipment Page Page Switch and Jumper Settings Base I/O Address and Interrupt Selection Talk/Listen Modes Talk/Listen Address and Special Function Selection Page Installation Special Considerations When Using the GPIB-COM filename Page Function Description Section Three GPIB-COM User Manual 3-2 National Instruments Corporation Figure 3-1 shows a block diagram of the GPIB-COM. GPIB Figure 3-1. Block Diagram of GPIB-COM GPIB-COM Components Page Section Four Running Diagnostic Tests The GPIB-COM Test Commands -1 printer test -2 plotter test -c change COM configuration -q quit Section Five Programming the GPIB-COM The GPIB-COM Registers Transmitter Holding Register Receive Buffer Register Divisor Latch Least Significant Byte (LSB) Register Divisor Latch Most Significant Byte (MSB) Register Interrupt Enable Register Page Interrupt Identification Register Line Control Register Page Modem Control Register Page Line Status Register Page Modem Status Register Page Programming the Serial Adapter Polling Method Interrupt-Driven Method The GPIB-COM Controller Function Appendix A Specifications Page Multiline Interface Messages Hex Oct Dec ASCII Msg Hex Oct Dec ASCII Msg Message Definitions Multiline Interface Messages Hex Oct Dec ASCII Msg Hex Oct Dec ASCII Msg Appendix C Operation of the GPIB History of the GPIB Types of Messages Talkers, Listeners, and Controllers System Controller and Active Controller GPIB Signals Appendix C Operation of the GPIB National Instruments Corporation C-3 GPIB-COM User Manual Figure C-1 shows the arrangement of these signals on the GPIB cable connector. Data Lines Handshake Lines NRFD (not ready for data) NDAC (not data accepted) Page Page Page Configuration Restrictions User Comment Form