Part 2

626 Interface Concepts( HP-IB DEVICE CAPABILITIES ILISTENERA device which is capable of receiving data over the interfacebus when addressed. A LISTENER becomes an ACTIVELISTENER when it is addressed by the controller.There can be up to 14 active listeners simultaneously on the interface.Some examples of listeners are printers, display devices,programmable power supplies, etc.TALKERA device which is capable of transmitting data over the interfacebus when addressed. A TALKER becomes an ACTIVE TALKERwhen it is addressed by the controller.There can be only one active talker on the bus at a time. Examplesof talkers are tape readers, voltmeters and counters thatare outputting data, etc.CONTROLLERA device which is capable of specifying talker and listener(s) foran information transfer. There can be two types of controllers,ACTIVE CONTROLLERS and a SYSTEM CONTROLLER. The activecontroller is the current controlling device. The system controllercan take control of the HP-IB even if it is not the activecontroller.There can only be one active controller on the interface at atime. If there is more than one controller on the HP-IB, only onecan be the system controller. A computer with an inputloutputcard is an example of a controller.HP-IB MessagesDifferent types of information can be passed over the HP-IB to one or more devices.One type of information is called a BUS MESSAGE. There are 12 bus messages forthe HP-IB and each bus message can be divided into three parts: (1 an operationportion (2) the address specified by the controller and (3) the information in themessage.The operation mnemonic portion of a bus message tells what action to take (CLEAR,LOCAL, etc.). Each HP-IB compatible controller has an equivalent syntax (which iscontroller-dependent) for the operation mnemonic. The address portion of a busmessage consists of an interface select code (ISC) and a device selector. The informationportion consists of the commands or data.Artisan Technology Group - Quality Instrumentation ... Guaranteed | (888) 88-SOURCE | www.artisantg.com