Black Box IC026AE-R2, IC026A-R2 manual Handshake Lines, Data Valid DAV

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CHAPTER 6: IEEE 488 Primer

6.5 Handshake Lines

The GPIB uses three handshake lines in an “I’m ready—Here’s the data—I’ve got it” sequence. This handshake protocol assures reliable data transfer, at the rate determined by the slowest Listener. One line is controlled by the Talker, while the other two are shared by all Active Listeners. The handshake lines, like the other IEEE 488 lines, are active low.

6.5.1 DATA VALID (DAV)

The DAV line is controlled by the Talker. The Talker verifies that NDAC is asserted (active low) which indicates that all Listeners have accepted the previous data byte transferred. The Talker then outputs data on the bus and waits until NRFD is unasserted (high) which indicates that all Addressed Listeners are ready to accept the information. When NRFD and NDAC are in the proper state, the Talker asserts DAV (active low) to indicate that the data on the bus is valid.

6.5.2NOT READY FOR DATA (NRFD)

This line is used by the Listeners to inform the Talker when they are ready to accept new data. The Talker must wait for each Listener to unassert this line (high), which they will do at their own rate when they are ready for more data. This assures that all devices that are to accept the information are ready to receive it.

6.5.3NOT DATA ACCEPTED (NDAC)

The NDAC line is also controlled by the Listeners. This line indicates to the Talker that each device addressed to listen has accepted the information. Each device releases NDAC (high) at its own rate, but the NDAC will not go high until the slowest Listener has accepted the data byte.

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Contents RS-232↔IEEE Interface Converter RS-232↔IEEE 488 Interface Converter Trademarks Used in this Manual RS-232↔IEEE 488 Interface Converter NOM Statement RS-232↔IEEE 488 Interface Converter Contents RS-232↔IEEE 488 Interface Converter Contents Specifications IEEE-488 InterfaceSerial Interface General SpecificationsDescription IntroductionAbbreviations Getting Started ConfigurationInspection Serial PortSW3 Serial Port Settings Switch SW1 Selecting the Serial Baud Rate Switch SW1 Selecting the Serial Word Length Data Bits Switch SW2 Selecting the Serial Parity Switch SW1 Selecting the Serial Handshake Selecting Terminator Substitution Switch SW2 Selecting the Serial TerminatorSwitch SW3 Selecting the Ieee Bus Terminator Selecting the ModeSelecting the Ieee Address 10. Switch SW2 Selecting the ModeFeature Selections Serial Interface 15. Selecting RS-232 or RS-422 Signal Levels TxD Transmit Data-Output-Pin RxD Receive Data-Input-PinClear To Send-Input-Pin Request To Send-Output-PinGnd Ground-Pin Vtest Test Voltage-Output-Pin+RxD Receive Data Plus-Input-Pin +TxD Transmit Data Plus-Output-PinRTS CTS DSR RTS CTS GeneralGetting Started Controller-Mode Serial to Ieee Operation Controller OperationSerial and Ieee Terminator Substitution Ieee Address Selection Talk-Back FeaturesSwitch SW1 Enabling or Disabling Talk-Back on Terminator Switch SW2 Enabling or Disabling Talk-Back on Timeout SP1PA1000,1000PDPA1000,6000PUSP0 7470APlotter Applications A PC-Based Graphics System SW3 MacPlot Configuration Screen Setting the Internal DIP Shorting Jumper for RS-422 SW3 Printer Applications Peripheral Operation Peripheral-Mode OperationSerial and Ieee Input Buffers Ieee Data Transfers Controlled BUS Data Transfers DIO8 Ieee Input Buffer not Empty Serial-Poll Status-Byte RegisterNot Defined-Always RsvSerial Input Buffer not Empty Ieee Input Buffer FullIeee 488 Bus Implementation Use of Serial and Bus TerminatorsUntalk UNT SW3 View for Ieee Address Selection Ieee 488 Primer HistoryGeneral Structure RS-232↔IEEE 488 Interface Converter DMM Send It to My AddressBus Management Lines Data Valid DAV Handshake LinesData Lines Multiline CommandsTalk Address Group TAG More on Service Requests Serial Poll Address Device Part Number Function Theory of OperationComponent Layout of the Interface Converter’s Motherboard Board LayoutRED BLK CLS Appendix A. Sample Dumb-Terminal ProgramSOH Multiline MessagesAscii Character How To Read the ChartDIO1 DIO2 DIO3 IndexIndex SW1 Copyright 1998. Black Box Corporation. All rights reserved