Black Box IC026A-R2, IC026AE-R2 manual More on Service Requests

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RS-232↔IEEE 488 INTERFACE CONVERTER

6.7.12TAKE CONTROL (TCT)

This command passes bus control responsibilities from the current Controller to another device which has the ability to control. ($09 )

6.7.13SECONDARY COMMAND GROUP (SCG)

These are any one of the 32 possible commands (0 to 31) in this group. They must immediately follow a talk or listen address. ($60 to $7F)

6.7.14PARALLEL POLL CONFIGURE (PPC)

For devices capable of performing a Parallel Poll, this command determines which data bit they are to assert in response to a Parallel Poll ($05)

6.7.15PARALLEL POLL UNCONFIGURE (PPU)

This disables all devices from responding to a Parallel Poll. ($15)

6.8 More on Service Requests

Most of the commands covered, both uniline and multiline, are the responsibility of the Active Controller to send and the bus devices to recognize. Most of these happen routinely by the interface and are totally transparent to the system programmer. Other commands are used directly by the user to provide optimum system control. Of the uniline commands, SRQ is very important to the test system, and the software designer has easy access to this line by most devices. Service Request is the method by which a bus device can signal to the Controller that an event has occurred. It is similar to an interrupt in a microprocessor-based system.

Most intelligent bus peripherals have the ability to assert SRQ. A DMM might assert it when its measurement is complete, if its input is overloaded or for any of an assortment of reasons. A power supply might SRQ if its output has current limited. This is a powerful bus feature that removes the burden from the System Controller to periodically inquire, “Are you done yet?” Instead, the Controller says, “Do what I told you to do and let me know when you’re done” or “Tell me when something is wrong.”

Since SRQ is a single line command, there is no way for the Controller to determine which device requested the service without additional information. This information is provided by the multiline commands for Serial Poll and Parallel Poll.

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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 Specifications GeneralIntroduction DescriptionAbbreviations Configuration Getting StartedInspection 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 Switch SW2 Selecting the Serial Terminator Selecting Terminator SubstitutionSelecting the Mode Switch SW3 Selecting the Ieee Bus Terminator10. Switch SW2 Selecting the Mode Selecting the Ieee AddressFeature Selections Serial Interface 15. Selecting RS-232 or RS-422 Signal Levels RxD Receive Data-Input-Pin TxD Transmit Data-Output-PinClear To Send-Input-Pin Request To Send-Output-PinVtest Test Voltage-Output-Pin Gnd Ground-Pin+RxD Receive Data Plus-Input-Pin +TxD Transmit Data Plus-Output-PinRTS CTS General DSR RTS CTSGetting Started Controller Operation Controller-Mode Serial to Ieee OperationSerial and Ieee Terminator Substitution Talk-Back Features Ieee Address SelectionSwitch SW1 Enabling or Disabling Talk-Back on Terminator Switch SW2 Enabling or Disabling Talk-Back on Timeout 7470A SP1PA1000,1000PDPA1000,6000PUSP0Plotter 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 Serial-Poll Status-Byte Register DIO8 Ieee Input Buffer not EmptyRsv Not Defined-AlwaysSerial Input Buffer not Empty Ieee Input Buffer FullUse of Serial and Bus Terminators Ieee 488 Bus ImplementationUntalk UNT SW3 View for Ieee Address Selection Ieee 488 Primer HistoryGeneral Structure RS-232↔IEEE 488 Interface Converter Send It to My Address DMMBus Management Lines Handshake Lines Data Valid DAVMultiline Commands Data LinesTalk Address Group TAG More on Service Requests Serial Poll Theory of Operation Address Device Part Number FunctionBoard Layout Component Layout of the Interface Converter’s MotherboardRED BLK Appendix A. Sample Dumb-Terminal Program CLSMultiline Messages SOHHow To Read the Chart Ascii CharacterIndex DIO1 DIO2 DIO3Index SW1 Copyright 1998. Black Box Corporation. All rights reserved