Model 7002Switch System Instruction Manual - Advanced Test ...

IEEE-488 Bus Overviewdevice will release NDAC at its own rate, but NDAC will notbe released to go high until all devices have accepted the databyte.The sequence just described is used to transfer both data, talkand listen addresses, as well as multiline commands. Thestate of the ATN line determines whether the data bus containsdata, addresses or commands as described in the followingparagraph.˛Bus CommandsThe instrument may be given a number of special bus commandsthrough the IEEE-488 interface. This section brieflydescribes the purpose of the bus commands which aregrouped into the following three categories.1. Uniline Commands — Sent by setting the associated buslines true. For example, to assert REN (Remote Enable),the REN line would be set low (true).2. Multiline Commands — General bus commands whichare sent over the data lines with the ATN line true (low).3. Common Commands — Commands that are common toall devices on the bus; sent with ATN high (false).4. SCPI Commands — Commands that are particular toeach device on the bus; sent with ATN (false).These bus commands and their general purpose are summarizedin Table D-1.Table D-1IEEE-488 bus command summaryCommandtypeCommandState ofATNlineCommentsUnilineREN (Remote Enable)EOIIFC (Interface Clear)ATN (Attention)SRQXXXLowXSet up devices for remote operation.Marks end of transmission.Clears interface.Defines data bus contents.Controlled by external device.MultilineUniversalLLO (Local Lockout)DCL (Device Clear)SPE (Serial Enable)SPD (Serial Poll Disable)LowLowLowLowLocks our local operation.Returns device to default conditions.Enables serial polling.Disables serial polling.AddressedSDC (Selective Device Clear)GTL (Go To Local)LowLowReturns unit to default conditions.Returns device to local.UnaddressedUNL (Unlisten)UNT (Untalk)LowLowRemoves all listeners from the bus.Removes any talkers from the bus.Common — High Programs IEEE-488.2 compatible instruments forcommon operations.SCPI — High Programs SCPI compatible instruments for particularoperations.D-4